Systems and methods for calibrating a switched mode ion energy distribution system

ABSTRACT

Systems, methods and apparatus for regulating ion energies and ion energy distributions along with calibrating a bias source and a plasma processing chamber are disclosed. An exemplary method includes applying a periodic voltage function to a load emulator, which emulates electrical characteristics of a plasma load and associated electronics such as an e-chuck. The load emulator can be measured for various electrical parameters and compared to expected parameters generated by the bias source. Differences between measured and expected values can be used to identify and correct faults and abnormalities in the bias supply, the chamber, or a power source used to ignite and sustain the plasma. Once the bias supply is calibrated, the chamber can be calibrated by measuring and calculating an effective capacitance comprising a series and parallel capacitance of the substrate support and optionally the substrate.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to plasma processing. Inparticular, but not by way of limitation, the present invention relatesto methods and apparatuses for plasma-assisted etching, deposition,and/or other plasma-assisted processes.

BACKGROUND OF THE DISCLOSURE

Many types of semiconductor devices are fabricated using plasma-basedetching techniques. If it is a conductor that is etched, a negativevoltage with respect to ground may be applied to the conductivesubstrate so as to create a substantially uniform negative voltageacross the surface of the substrate conductor, which attracts positivelycharged ions toward the conductor, and as a consequence, the positiveions that impact the conductor have substantially the same energy.

If the substrate is a dielectric, however, a non-varying voltage isineffective to place a voltage across the surface of the substrate. Butan AC voltage (e.g., high frequency) may be applied to the conductiveplate (or chuck) so that the AC field induces a voltage on the surfaceof the substrate. During the positive half of the AC cycle, thesubstrate attracts electrons, which are light relative to the mass ofthe positive ions; thus many electrons will be attracted to the surfaceof the substrate during the positive part of the cycle. As aconsequence, the surface of the substrate will be charged negatively,which causes ions to be attracted toward the negatively-charged surface.And when the ions impact the surface of the substrate, the impactdislodges material from the surface of the substrate—effectuating theetching.

In many instances, it is desirable to have a narrow ion energydistribution, but applying a sinusoidal waveform to the substrateinduces a broad distribution of ion energies, which limits the abilityof the plasma process to carry out a desired etch profile. Knowntechniques to achieve a narrow ion energy distribution are expensive,inefficient, difficult to control, and may adversely affect the plasmadensity. As a consequence, these known techniques have not beencommercially adopted. Accordingly, a system and method are needed toaddress the shortfalls of present technology and to provide other newand innovative features.

SUMMARY

Illustrative embodiments of the present disclosure that are shown in thedrawings are summarized below. These and other embodiments are morefully described in the Detailed Description section. It is to beunderstood, however, that there is no intention to limit the inventionto the forms described in this Summary of the Invention or in theDetailed Description. One skilled in the art can recognize that thereare numerous modifications, equivalents, and alternative constructionsthat fall within the spirit and scope of the invention as expressed inthe claims.

Some embodiments of the disclosure may be characterized as a method ofcalibrating a bias supply configured to generate a potential on a topsurface of a substrate during plasma processing of the substrate. Themethod can include receiving a modified periodic voltage functioncomprising pulses and a portion between the pulses. The method may alsoinclude receiving an expected ion energy and receiving an expected ioncurrent. The method may further include delivering the modified periodicvoltage function to a plasma load emulator. The method can furtherinclude measuring a voltage across a sheath capacitance component of theplasma load emulator. The method may also include applying a knowncurrent from a current source of the plasma load emulator to the sheathcapacitance component. The method may further include applying a knowncurrent from a current source of the plasma load emulator to the sheathcapacitance component. The method may also include comparing the voltageacross the sheath capacitance component to the expected ion energy anddetermining an ion energy error from this comparing. The method furthermay include comparing the current to the expected ion current anddetermining an ion current error from this comparing. Finally, themethod may include reporting the ion energy error and the ion currenterror.

Other embodiments of the disclosure may also be characterized as asystem comprising a bias supply and a calibration component. The biassupply can include a power supply, an ion current compensationcomponent, and a controller. The calibration component can include aload emulator, a measurement component, and an analysis component. Thepower supply can be configured to provide a periodic voltage function.The ion current compensation component can be configured to modify theperiodic voltage function with an ion compensation current so that thebias supply provides the modified periodic voltage function. Thecontroller can be configured to provide instructions to the power supplyto adjust the periodic voltage function and to provide instructions tothe ion current compensation component to adjust the ion compensationcurrent. The load emulator can have circuitry configured to emulate aplasma load. The load emulator can further be configured to receive themodified periodic voltage function. The measurement component can beconfigured to make one or more measurements of the modified periodicvoltage function as it interacts with the circuitry of the loademulator. The analysis component can be configured to determine an ioncurrent error by comparing at least one measured value from themeasurement component and at least one expected value from the biassupply.

Other embodiments of the disclosure can be characterized as a systemcomprising a bias supply and a calibration component. The bias supplycan generate a modified periodic voltage function, wherein the modifiedperiodic voltage function comprises periodic pulses with a slopedportion between the pulses, wherein the slope of the sloped portionbetween the pulses is controlled via an ion compensation current. Thecalibration component can receive the modified periodic voltage functionand measure a voltage and a current of the modified periodic voltagefunction in the load emulator. Furthermore, the voltage can emulate asubstrate voltage associated with a plasma load and the current canemulate an ion current in the plasma load.

Other embodiments of the disclosure may also be characterized as acalibration component comprising a load emulator, a measurementcomponent, and an analysis component. The load emulator may beconfigured to receive a modified periodic voltage function. Themeasurement component can be configured to measure at least a currentand a voltage within the load emulator as the modified periodic voltagefunction interacts with circuitry within the load emulator. The analysiscomponent can be configured to compare the measured current and themeasured voltage to an expected current and an expected voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

Various objects and advantages and a more complete understanding of thepresent invention are apparent and more readily appreciated by referringto the following detailed description and to the appended claims whentaken in conjunction with the accompanying drawings:

FIG. 1 illustrates a block diagram of a plasma processing system inaccordance with one implementation of the present invention;

FIG. 2 is a block diagram depicting an exemplary embodiment of theswitch-mode power system depicted in FIG. 1;

FIG. 3 is a schematic representation of components that may be utilizedto realize the switch-mode bias supply described with reference to FIG.2;

FIG. 4 is a timing diagram depicting two drive signal waveforms;

FIG. 5 is a graphical representation of a single mode of operating theswitch mode bias supply, which effectuates an ion energy distributionthat is concentrated at a particular ion energy;

FIG. 6 are graphs depicting a bi-modal mode of operation in which twoseparate peaks in ion energy distribution are generated;

FIGS. 7A and 7B are is are graphs depicting actual, direct ion energymeasurements made in a plasma;

FIG. 8 is a block diagram depicting another embodiment of the presentinvention;

FIG. 9A is a graph depicting an exemplary periodic voltage function thatis modulated by a sinusoidal modulating function;

FIG. 9B is an exploded view of a portion of the periodic voltagefunction that is depicted in FIG. 9A;

FIG. 9C depicts the resulting distribution of ion energies, ontime-averaged basis, that results from the sinusoidal modulation of theperiodic voltage function;

FIG. 9D depicts actual, direct, ion energy measurements made in a plasmaof a resultant, time averaged, IEDF when a periodic voltage function ismodulated by a sinusoidal modulating function;

FIG. 10A depicts a periodic voltage function is modulated by a sawtoothmodulating function;

FIG. 10B is an exploded view of a portion of the periodic voltagefunction that is depicted in FIG. 10A;

FIG. 10C is a graph depicting the resulting distribution of ionenergies, on a time averaged basis, that results from the sinusoidalmodulation of the periodic voltage function in FIGS. 10A and 10B;

FIG. 11 are graphs showing IEDF functions in the right column andassociated modulating functions in the left column;

FIG. 12 is a block diagram depicting an embodiment in which an ioncurrent compensation component compensates for ion current in a plasmachamber;

FIG. 13 is a diagram depicting an exemplary ion current compensationcomponent;

FIG. 14 is a graph depicting an exemplary voltage at node Vo depicted inFIG. 13;

FIGS. 15A-15C are voltage waveforms as appearing at the surface of thesubstrate or wafer responsive to compensation current;

FIG. 16 is an exemplary embodiment of a current source, which may beimplemented to realize the current source described with reference toFIG. 13;

FIGS. 17A and 17B are block diagrams depicting other embodiments of thepresent invention;

FIG. 18 is a block diagram depicting yet another embodiment of thepresent invention;

FIG. 19 is a block diagram depicting still another embodiment of thepresent invention;

FIG. 20 is a block diagram input parameters and control outputs that maybe utilized in connection with the embodiments described with referenceto FIGS. 1-19;

FIG. 21 is a block diagram depicting yet another embodiment of thepresent invention;

FIG. 22 is a block diagram depicting yet another embodiment of thepresent invention;

FIG. 23 is a block diagram depicting yet another embodiment of thepresent invention;

FIG. 24 is a block diagram depicting yet another embodiment of thepresent invention;

FIG. 25 is a block diagram depicting yet another embodiment of thepresent invention;

FIG. 26 is a block diagram depicting yet another embodiment of thepresent invention;

FIG. 27 is a block diagram depicting yet another embodiment of thepresent invention;

FIG. 28 illustrates a method according to an embodiment of thisdisclosure;

FIG. 29 illustrates another method according to an embodiment of thisdisclosure;

FIG. 30 illustrates one embodiment of a method of controlling an ionenergy distribution of ions impacting a surface of a substrate;

FIG. 31 illustrates methods for setting the IEDF and the ion energy;

FIG. 32 illustrates two modified periodic voltage function waveformsdelivered to the substrate support according to one embodiment of thisdisclosure;

FIG. 33 illustrates an ion current waveform that can indicate plasmasource instability or changes in the plasma density;

FIG. 34 illustrates an ion current, I_(I), of a modified periodicvoltage function waveform having a non-cyclical shape;

FIG. 35 illustrates a modified periodic voltage function waveform thatcan indicate faults within the bias supply;

FIG. 36 illustrates a modified periodic voltage function waveform thatcan be indicative of a dynamic change in the system capacitance;

FIG. 37 illustrates a modified periodic voltage function waveform thatmay be indicative of changes in plasma density;

FIG. 38 illustrates a sampling of ion current for different processruns, where drift in the ion current can indicate system drift;

FIG. 39 illustrates a sampling of ion current for different processparameters.

FIG. 40 illustrates two bias waveforms monitored without a plasma in thechamber;

FIG. 41 illustrates two bias waveforms that can be used to validate aplasma process;

FIG. 42 illustrates a number of power supply voltages and ion energyplots showing the relationship between the power supply voltage and ionenergy;

FIG. 43 illustrates one embodiment of a method of controlling an ionenergy distribution of ions impacting a surface of a substrate;

FIG. 44 illustrates various waveforms at different points in the systemsherein disclosed;

FIG. 45 illustrates the effects of making a final incremental change inion current compensation, Ic, in order to match it to ion current I_(I);

FIG. 46 illustrates selection of ion energy;

FIG. 47 illustrates selection and expansion of the ion energydistribution function width;

FIG. 48 illustrates one pattern of the power supply voltage, V_(PS),that can be used to achieve more than one ion energy level where eachion energy level has a narrow IEDF width;

FIG. 49 illustrates another pattern of the power supply voltage, V_(PS),that can be used to achieve more than one ion energy level where eachion energy level has a narrow IEDF width; and

FIG. 50 illustrates one combination of power supply voltages, V_(PS),and ion current compensation, I_(C), that can be used to create adefined IEDF.

FIG. 51 illustrates a schematic diagram depicting an exemplaryembodiment of an apparatus for calibrating a bias supply.

FIG. 52 illustrates a load emulator of the calibration componentillustrated in FIG. 51.

FIG. 53 illustrates a method of calibrating a bias supply.

FIG. 54 illustrates another method of calibrating a bias supply.

FIG. 55 illustrates an embodiment of a system for calibrating a plasmaprocessing chamber.

FIG. 56 illustrates a method for calibrating the plasma processingchamber of FIG. 55.

FIG. 57 illustrates another method for calibrating the plasma processingchamber of FIG. 55.

DETAILED DESCRIPTION

An exemplary embodiment of a plasma processing system is shown generallyin FIG. 1. As depicted, a plasma power supply 102 is coupled to a plasmaprocessing chamber 104 and a switch-mode power supply 106 is coupled toa support 108 upon which a substrate 110 rests within the chamber 104.Also shown is a controller 112 that is coupled to the switch-mode powersupply 106.

In this exemplary embodiment, the plasma processing chamber 104 may berealized by chambers of substantially conventional construction (e.g.,including a vacuum enclosure which is evacuated by a pump or pumps (notshown)). And, as one of ordinary skill in the art will appreciate, theplasma excitation in the chamber 104 may be by any one of a variety ofsources including, for example, a helicon type plasma source, whichincludes magnetic coil and antenna to ignite and sustain a plasma 114 inthe reactor, and a gas inlet may be provided for introduction of a gasinto the chamber 104.

As depicted, the exemplary plasma chamber 104 is arranged and configuredto carry out plasma-assisted etching of materials utilizing energeticion bombardment of the substrate 110, and other plasma processing (e.g.,plasma deposition and plasma assisted ion implantation). The plasmapower supply 102 in this embodiment is configured to apply power (e.g.,RF power) via a matching network (not shown)) at one or more frequencies(e.g., 13.56 MHz) to the chamber 104 so as to ignite and sustain theplasma 114. It should be understood that the present invention is notlimited to any particular type of plasma power supply 102 or source tocouple power to the chamber 104, and that a variety of frequencies andpower levels may be may be capacitively or inductively coupled to theplasma 114.

As depicted, a dielectric substrate 110 to be treated (e.g., asemiconductor wafer), is supported at least in part by a support 108that may include a portion of a conventional wafer chuck (e.g., forsemiconductor wafer processing). The support 108 may be formed to havean insulating layer between the support 108 and the substrate 110 withthe substrate 110 being capacitively coupled to the platforms but mayfloat at a different voltage than the support 108.

As discussed above, if the substrate 110 and support 108 are conductors,it is possible to apply a non-varying voltage to the support 108, and asa consequence of electric conduction through the substrate 110, thevoltage that is applied to the support 108 is also applied to thesurface of the substrate 110.

When the substrate 110 is a dielectric, however, the application of anon-varying voltage to the support 108 is ineffective to place a voltageacross the treated surface of the substrate 110. As a consequence, theexemplary switch-mode power supply 106 is configured to be controlled soas to effectuate a voltage on the surface of the substrate 110 that iscapable of attracting ions in the plasma 114 to collide with thesubstrate 110 so as to carry out a controlled etching and/or depositionof the substrate 110, and/or other plasma-assisted processes.

Moreover, as discussed further herein, embodiments of the switch-modepower supply 106 are configured to operate so that there is aninsubstantial interaction between the power applied (to the plasma 114)by the plasma power supply 102 and the power that is applied to thesubstrate 110 by the switch-mode power supply 106. The power applied bythe switch-mode power supply 106, for example, is controllable so as toenable control of ion energy without substantially affecting the densityof the plasma 114.

Furthermore, many embodiments of the exemplary switch-mode supply 106depicted in FIG. 1 are realized by relatively inexpensive componentsthat may be controlled by relatively simple control algorithms. And ascompared to prior art approaches, many embodiments of the switch modepower supply 106 are much more efficient; thus reducing energy costs andexpensive materials that are associated with removing excess thermalenergy.

One known technique for applying a voltage to a dielectric substrateutilizes a high-power linear amplifier in connection with complicatedcontrol schemes to apply power to a substrate support, which induces avoltage at the surface of the substrate. This technique, however, hasnot been adopted by commercial entities because it has not proven to becost effective nor sufficiently manageable. In particular, the linearamplifier that is utilized is typically large, very expensive,inefficient, and difficult to control. Furthermore, linear amplifiersintrinsically require AC coupling (e.g., a blocking capacitor) andauxiliary functions like chucking are achieved with a parallel feedcircuit which harms AC spectrum purity of the system for sources with achuck.

Another technique that has been considered is to apply high frequencypower (e.g., with one or more linear amplifiers) to the substrate. Thistechnique, however, has been found to adversely affect the plasmadensity because the high frequency power that is applied to thesubstrate affects the plasma density.

In some embodiments, the switch-mode power supply 106 depicted in FIG. 1may be realized by buck, boost, and/or buck-boost type powertechnologies. In these embodiments, the switch-mode power supply 106 maybe controlled to apply varying levels of pulsed power to induce apotential on the surface of the substrate 110.

In other embodiments, the switch-mode power supply 106 is realized byother more sophisticated switch mode power and control technologies.Referring next to FIG. 2, for example, the switch-mode power supplydescribed with reference to FIG. 1 is realized by a switch-mode biassupply 206 that is utilized to apply power to the substrate 110 toeffectuate one or more desired energies of the ions that bombard thesubstrate 110. Also shown are an ion energy control component 220, anarc detection component 222, and a controller 212 that is coupled toboth the switch-mode bias supply 206 and a waveform memory 224.

The illustrated arrangement of these components is logical; thus thecomponents can be combined or further separated in an actualimplementation, and the components can be connected in a variety of wayswithout changing the basic operation of the system. In some embodimentsfor example, the controller 212, which may be realized by hardware,software, firmware, or a combination thereof, may be utilized to controlboth the power supply 202 and switch-mode bias supply 206. Inalternative embodiments, however, the power supply 202 and theswitch-mode bias supply 206 are realized by completely separatedfunctional units. By way of further example, the controller 212,waveform memory 224, ion energy control portion 220 and the switch-modebias supply 206 may be integrated into a single component (e.g.,residing in a common housing) or may be distributed among discretecomponents.

The switch-mode bias supply 206 in this embodiment is generallyconfigured to apply a voltage to the support 208 in a controllablemanner so as to effectuate a desired (or defined) distribution of theenergies of ions bombarding the surface of the substrate. Morespecifically, the switch-mode bias supply 206 is configured toeffectuate the desired (or defined) distribution of ion energies byapplying one or more particular waveforms at particular power levels tothe substrate. And more particularly, responsive to an input from theion energy control portion 220, the switch-mode bias supply 206 appliesparticular power levels to effectuate particular ion energies, andapplies the particular power levels using one or more voltage waveformsdefined by waveform data in the waveform memory 224. As a consequence,one or more particular ion bombardment energies may be selected with theion control portion to carry out controlled etching of the substrate (orother forms of plasma processing).

As depicted, the switch-mode power supply 206 includes switch components226′, 226″ (e.g., high power field effect transistors) that are adaptedto switch power to the support 208 of the substrate 210 responsive todrive signals from corresponding drive components 228′, 228″. And thedrive signals 230′, 230″ that are generated by the drive components228′, 228″ are controlled by the controller 212 based upon timing thatis defined by the content of the waveform memory 224. For example, thecontroller 212 in many embodiments is adapted to interpret the contentof the waveform memory and generate drive-control signals 232′, 232″,which are utilized by the drive components 228′, 228″ to control thedrive signals 230′, 230″ to the switching components 226′, 226″.Although two switch components 226′, 226″, which may be arranged in ahalf-bridge configuration, are depicted for exemplary purposes, it iscertainly contemplated that fewer or additional switch components may beimplemented in a variety of architectures (e.g., an H-bridgeconfiguration).

In many modes of operation, the controller 212 (e.g., using the waveformdata) modulates the timing of the drive-control signals 232′, 232″ toeffectuate a desired waveform at the support 208 of the substrate 210.In addition, the switch mode bias supply 206 is adapted to supply powerto the substrate 210 based upon an ion-energy control signal 234, whichmay be a DC signal or a time-varying waveform. Thus, the presentembodiment enables control of ion distribution energies by controllingtiming signals to the switching components and controlling the power(controlled by the ion-energy control component 220) that is applied bythe switching components 226′, 226″.

In addition, the controller 212 in this embodiment is configured,responsive to an arc in the plasma chamber 204 being detected by the arcdetection component 222, to carry out arc management functions. In someembodiments, when an arc is detected the controller 212 alters thedrive-control signals 232′, 232″ so that the waveform applied at theoutput 236 of the switch mode bias supply 206 extinguishes arcs in theplasma 214. In other embodiments, the controller 212 extinguishes arcsby simply interrupting the application of drive-control signals 232′,232″ so that the application of power at the output 236 of theswitch-mode bias supply 206 is interrupted.

Referring next to FIG. 3, it is a schematic representation of componentsthat may be utilized to realize the switch-mode bias supply 206described with reference to FIG. 2. As shown, the switching componentsT1 and T2 in this embodiment are arranged in a half-bridge (alsoreferred to as or totem pole) type topology. Collectively, R2, R3, C1,and C2 represent a plasma load, C10 is an effective capacitance (alsoreferred to herein as a series capacitance or a chuck capacitance), andC3 is an optional physical capacitor to prevent DC current from thevoltage induced on the surface of the substrate or from the voltage ofan electrostatic chuck (not shown) from flowing through the circuit. C10is referred to as the effective capacitance because it includes theseries capacitance (or also referred to as a chuck capacitance) of thesubstrate support and the electrostatic chuck (or e-chuck) as well asother capacitances inherent to the application of a bias such as theinsulation and substrate. As depicted, L1 is stray inductance (e.g., thenatural inductance of the conductor that feeds the power to the load).And in this embodiment, there are three inputs: Vbus, V2, and V4.

V2 and V4 represent drive signals (e.g., the drive signals 230′, 230″output by the drive components 228′, 228″ described with reference toFIG. 2), and in this embodiment, V2 and V4 can be timed (e.g., thelength of the pulses and/or the mutual delay) so that the closure of T1and T2 may be modulated to control the shape of the voltage output Vout,which is applied to the substrate support. In many implementations, thetransistors used to realize the switching components T1 and T2 are notideal switches, so to arrive at a desired waveform, thetransistor-specific characteristics are taken into consideration. Inmany modes of operation, simply changing the timing of V2 and V4 enablesa desired waveform to be applied at Vout.

For example, the switches T1, T2 may be operated so that the voltage atthe surface of the substrate 110, 210 is generally negative withperiodic voltage pulses approaching and/or slightly exceeding a positivevoltage reference. The value of the voltage at the surface of thesubstrate 110, 210 is what defines the energy of the ions, which may becharacterized in terms of an ion energy distribution function (IEDF). Toeffectuate desired voltage(s) at the surface of the substrate 110, 210,the pulses at Vout may be generally rectangular and have a width that islong enough to induce a brief positive voltage at the surface of thesubstrate 110, 210 so as to attract enough electrons to the surface ofthe substrate 110, 210 in order to achieve the desired voltage(s) andcorresponding ion energies.

The periodic voltage pulses that approach and/or slightly exceed thepositive voltage reference may have a minimum time limited by theswitching abilities of the switches T1, T2. The generally negativeportions of the voltage can extend so long as the voltage does not buildto a level that damages the switches. At the same time, the length ofnegative portions of the voltage should exceed an ion transit time.

Vbus in this embodiment defines the amplitude of the pulses measured atVout, which defines the voltage at the surface of the substrate, and asa consequence, the ion energy. Referring briefly again to FIG. 2, Vbusmay be coupled to the ion energy control portion, which may be realizedby a DC power supply that is adapted to apply a DC signal or atime-varying waveform to Vbus.

The pulse width, pulse shape, and/or mutual delay of the two signals V2,V4 may be modulated to arrive at a desired waveform at Vout (alsoreferred to herein as a modified periodic voltage function), and thevoltage applied to Vbus may affect the characteristics of the pulses. Inother words, the voltage Vbus may affect the pulse width, pulse shapeand/or the relative phase of the signals V2, V4. Referring briefly toFIG. 4, for example, shown is a timing diagram depicting two drivesignal waveforms that may be applied to T1 and T2 (as V2 and V4) so asto generate the period voltage function at Vout as depicted in FIG. 4.To modulate the shape of the pulses at Vout (e.g. to achieve thesmallest time for the pulse at Vout, yet reach a peak value of thepulses) the timing of the two gate drive signals V2, V4 may becontrolled.

For example, the two gate drive signals V2, V4 may be applied to theswitching components T1, T2 so the time that each of the pulses isapplied at Vout may be short compared to the time T between pulses, butlong enough to induce a positive voltage at the surface of the substrate110, 210 to attract electrons to the surface of the substrate 110, 210.Moreover, it has been found that by changing the gate voltage levelbetween the pulses, it is possible to control the slope of the voltagethat is applied to Vout between the pulses (e.g., to achieve asubstantially constant voltage at the surface of the substrate betweenpulses). In some modes of operation, the repetition rate of the gatepulses is about 400 kHz, but this rate may certainly vary fromapplication to application.

Although not required, in practice, based upon modeling and refiningupon actual implementation, waveforms that may be used to generate thedesired (or defined) ion energy distributions may be defined, and thewaveforms can be stored (e.g., in the waveform memory portion describedwith reference to FIG. 1 as a sequence of voltage levels). In addition,in many implementations, the waveforms can be generated directly (e.g.,without feedback from Vout); thus avoiding the undesirable aspects of afeedback control system (e.g., settling time).

Referring again to FIG. 3, Vbus can be modulated to control the energyof the ions, and the stored waveforms may be used to control the gatedrive signals V2, V4 to achieve a desired pulse amplitude at Vout whileminimizing the pulse width. Again, this is done in accordance with theparticular characteristics of the transistors, which may be modeled orimplemented and empirically established. Referring to FIG. 5, forexample, shown are graphs depicting Vbus versus time, voltage at thesurface of the substrate 110, 210 versus time, and the corresponding ionenergy distribution.

The graphs in FIG. 5 depict a single mode of operating the switch modebias supply 106, 206, which effectuates an ion energy distribution thatis concentrated at a particular ion energy. As depicted, to effectuatethe single concentration of ion energies in this example, the voltageapplied at Vbus is maintained constant while the voltages applied to V2and V4 are controlled (e.g., using the drive signals depicted in FIG. 3)so as to generate pulses at the output of the switch-mode bias supply106, 206, which effectuates the corresponding ion energy distributionshown in FIG. 5.

As depicted in FIG. 5, the potential at the surface of the substrate110, 210 is generally negative to attract the ions that bombard and etchthe surface of the substrate 110, 210. The periodic short pulses thatare applied to the substrate 110, 210 (by applying pulses to Vout) havea magnitude defined by the potential that is applied to Vbus, and thesepulses cause a brief change in the potential of the substrate 110, 210(e.g., close to positive or slightly positive potential), which attractselectrons to the surface of the substrate to achieve the generallynegative potential along the surface of the substrate 110, 210. Asdepicted in FIG. 5, the constant voltage applied to Vbus effectuates asingle concentration of ion flux at particular ion energy; thus aparticular ion bombardment energy may be selected by simply setting Vbusto a particular potential. In other modes of operation, two or moreseparate concentrations of ion energies may be created (e.g., see FIG.49).

One of skill in the art will recognize that the power supply need not belimited to a switch-mode power supply, and as such the output of thepower supply can also be controlled in order to effect a certain ionenergy. As such, the output of the power supply, whether switch-mode orotherwise, when considered without being combined with an ion currentcompensation or an ion current, can also be referred to as a powersupply voltage, V_(PS).

Referring next to FIG. 6, for example, shown are graphs depicting abi-modal mode of operation in which two separate peaks in ion energydistribution are generated. As shown, in this mode of operation, thesubstrate experiences two distinct levels of voltages and periodicpulses, and as a consequence, two separate concentrations of ionenergies are created. As depicted, to effectuate the two distinct ionenergy concentrations, the voltage that is applied at Vbus alternatesbetween two levels, and each level defines the energy level of the twoion energy concentrations.

Although FIG. 6 depicts the two voltages at the substrate 110, 210 asalternating after every pulse (e.g., FIG. 48), this is certainly notrequired. In other modes of operation for example, the voltages appliedto V2 and V4 are switched (e.g., using the drive signals depicted inFIG. 3) relative to the voltage applied to Vout so that the inducedvoltage at surface of the substrate alternates from a first voltage to asecond voltage (and vice versa) after two or more pulses (e.g., FIG.49).

In prior art techniques, attempts have been made to apply thecombination of two waveforms (generated by waveform generators) to alinear amplifier and apply the amplified combination of the twowaveforms to the substrate in order to effectuate multiple ion energies.This approach, however, is much more complex then the approach describedwith reference to FIG. 6, and requires an expensive linear amplifier,and waveform generators.

Referring next to FIGS. 7A and 7B, shown are graphs depicting actual,direct ion energy measurements made in a plasma corresponding tomonoenergetic and dual-level regulation of the DC voltage applied toVbus, respectively. As depicted in FIG. 7A, the ion energy distributionis concentrated around 80 eV responsive to a non-varying application ofa voltage to Vbus (e.g., as depicted in FIG. 5). And in FIG. 7B, twoseparate concentrations of ion energies are present at around 85 eV and115 eV responsive to a dual-level regulation of Vbus (e.g., as depictedin FIG. 6).

Referring next to FIG. 8, shown is a block diagram depicting anotherembodiment of the present invention. As depicted, a switch-mode powersupply 806 is coupled to a controller 812, an ion-energy controlcomponent 820, and a substrate support 808 via an arc detectioncomponent 822. The controller 812, switch-mode supply 806, and ionenergy control component 820 collectively operate to apply power to thesubstrate support 808 so as to effectuate, on a time-averaged basis, adesired (or defined) ion energy distribution at the surface of thesubstrate 810.

Referring briefly to FIG. 9A for example, shown is a periodic voltagefunction with a frequency of about 400 kHz that is modulated by asinusoidal modulating function of about 5 kHz over multiple cycles ofthe periodic voltage function. FIG. 9B is an exploded view of theportion of the periodic voltage function that is circled in FIG. 9A, andFIG. 9C depicts the resulting distribution of ion energies, on atime-averaged basis, that results from the sinusoidal modulation of theperiodic voltage function. And FIG. 9D depicts actual, direct, ionenergy measurements made in a plasma of a resultant, time-averaged, IEDFwhen a periodic voltage function is modulated by a sinusoidal modulatingfunction. As discussed further herein, achieving a desired (or defined)ion energy distribution, on a time-averaged basis, may be achieved bysimply changing the modulating function that is applied to the periodicvoltage.

Referring to FIGS. 10A and 10B as another example, a 400 kHz periodicvoltage function is modulated by a sawtooth modulating function ofapproximately 5 kHz to arrive at the distribution of ion energiesdepicted in FIG. 10C on a time-averaged basis. As depicted, the periodicvoltage function utilized in connection with FIG. 10 is the same as inFIG. 9, except that the periodic voltage function in FIG. 10 ismodulated by a sawtooth function instead of a sinusoidal function.

It should be recognized that the ion energy distribution functionsdepicted in FIGS. 9C and 10C do not represent an instantaneousdistribution of ion energies at the surface of the substrate 810, butinstead represent the time average of the ion energies. With referenceto FIG. 9C, for example, at a particular instant in time, thedistribution of ion energies will be a subset of the depicteddistribution of ion energies that exist over the course of a full cycleof the modulating function.

It should also be recognized that the modulating function need not be afixed function nor need it be a fixed frequency. In some instances forexample, it may be desirable to modulate the periodic voltage functionwith one or more cycles of a particular modulating function toeffectuate a particular, time-averaged ion energy distribution, and thenmodulate the periodic voltage function with one or more cycles ofanother modulating function to effectuate another, time-averaged ionenergy distribution. Such changes to the modulating function (whichmodulates the periodic voltage function) may be beneficial in manyinstances. For example, if a particular distribution of ion energies isneeded to etch a particular geometric construct or to etch through aparticular material, a first modulating function may be used, and thenanother modulating function may subsequently be used to effectuate adifferent etch geometry or to etch through another material.

Similarly, the periodic voltage function (e.g., the 400 kHz componentsin FIGS. 9A, 9B, 10A, and 10B and Vout in FIG. 4) need not be rigidlyfixed (e.g., the shape and frequency of the periodic voltage functionmay vary), but generally its frequency is established by the transittime of ions within the chamber so that ions in the chamber are affectedby the voltage that is applied to the substrate 810.

Referring back to FIG. 8, the controller 812 provides drive-controlsignals 832′, 832″ to the switch-mode supply 806 so that the switch-modesupply 806 generates a periodic voltage function. The switch mode supply806 may be realized by the components depicted in FIG. 3 (e.g., tocreate a periodic voltage function depicted in FIG. 4), but it iscertainly contemplated that other switching architectures may beutilized.

In general, the ion energy control component 820 functions to apply amodulating function to the periodic voltage function (that is generatedby the controller 812 in connection with the switch mode power supply806). As shown in FIG. 8, the ion energy control component 820 includesa modulation controller 840 that is in communication with a custom IEDFportion 850, an IEDF function memory 848, a user interface 846, and apower component 844. It should be recognized that the depiction of thesecomponents is intended to convey functional components, which inreality, may be effectuated by common or disparate components.

The modulation controller 840 in this embodiment generally controls thepower component 844 (and hence its output 834) based upon data thatdefines a modulation function, and the power component 844 generates themodulation function 834 (based upon a control signal 842 from themodulation controller 840) that is applied to the periodic voltagefunction that is generated by the switch-mode supply 806. The userinterface 846 in this embodiment is configured to enable a user toselect a predefined IEDF function that is stored in the IEDF functionmemory 848, or in connection with the custom IEDF component 850, definea custom IEDF

In many implementations, the power component 844 includes a DC powersupply (e.g., a DC switch mode power supply or a linear amplifier),which applies the modulating function (e.g. a varying DC voltage) to theswitch mode power supply (e.g., to Vbus of the switch mode power supplydepicted in FIG. 3). In these implementations, the modulation controller840 controls the voltage level that is output by the power component 844so that the power component 844 applies a voltage that conforms to themodulating function.

In some implementations, the IEDF function memory 848 includes aplurality of data sets that correspond to each of a plurality of IEDFdistribution functions, and the user interface 846 enables a user toselect a desired (or defined) IEDF function. Referring to FIG. 11 forexample, shown in the right column are exemplary IEDF functions that maybe available for a user to select. And the left column depicts theassociated modulating function that the modulation controller 840 inconnection with the power component 844 would apply to the periodicvoltage function to effectuate the corresponding IEDF function. Itshould be recognized that the IEDF functions depicted in FIG. 11 areonly exemplary and that other IEDF functions may be available forselection.

The custom IEDF component 850 generally functions to enable a user, viathe user interface 846, to define a desired (or defined) ion energydistribution function. In some implementations for example, the customIEDF component 850 enables a user to establish values for particularparameters that define a distribution of ion energies.

For example, the custom IEDF component 850 may enable IEDF functions tobe defined in terms of a relative level of flux (e.g., in terms of apercentage of flux) at a high-level (IF-high), a mid-level (IF-mid), anda low level (IF-low) in connection with a function(s) that defines theIEDF between these energy levels. In many instances, only IF-high,IF-low, and the IEDF function between these levels is sufficient todefine an IEDF function. As a specific example, a user may request 1200eV at a 20% contribution level (contribution to the overall IEDF), 700eV at a 30% contribution level with a sinusoid IEDF between these twolevels.

It is also contemplated that the custom IEDF portion 850 may enable auser to populate a table with a listing of one or more (e.g., multiple)energy levels and the corresponding percentage contribution of eachenergy level to the IEDF. And in yet alternative embodiments, it iscontemplated that the custom IEDF component 850 in connection with theuser interface 846 enables a user to graphically generate a desired (ordefined) IEDF by presenting the user with a graphical tool that enablesa user to draw a desired (or defined) IEDF.

In addition, it is also contemplated that the IEDF function memory 848and the custom IEDF component 850 may interoperate to enable a user toselect a predefined IEDF function and then alter the predefined IEDFfunction so as to produce a custom IEDF function that is derived fromthe predefined IEDF function.

Once an IEDF function is defined, the modulation controller 840translates data that defines the desired (or defined) IEDF function intoa control signal 842, which controls the power component 844 so that thepower component 844 effectuates the modulation function that correspondsto the desired (or defined) IEDF. For example, the control signal 842controls the power component 844 so that the power component 844 outputsa voltage that is defined by the modulating function.

Referring next to FIG. 12, it is a block diagram depicting an embodimentin which an ion current compensation component 1260 compensates for ioncurrent in the plasma chamber 1204. Applicants have found that, athigher energy levels, higher levels of ion current within the chamberaffect the voltage at the surface of the substrate, and as aconsequence, the ion energy distribution is also affected. Referringbriefly to FIGS. 15A-15C for example, shown are voltage waveforms asthey appear at the surface of the substrate 1210 or wafer and theirrelationship to IEDF.

More specifically, FIG. 15A depicts a periodic voltage function at thesurface of the substrate 1210 when ion current I_(I) is equal tocompensation current Ic; FIG. 15B depicts the voltage waveform at thesurface of the substrate 1210 when ion current I_(I) is greater than thecompensation current Ic; and FIG. 15C depicts the voltage waveform atthe surface of the substrate when ion current is less than thecompensation current Ic.

As depicted in FIG. 15A, when I_(I)=Ic a spread of ion energies 1470 isrelatively narrow as compared to a uniform spread 1472 of ion energieswhen I_(I)>Ic as depicted in FIG. 15B or a uniform spread 1474 of ionenergies when I_(I)<Ic as depicted in FIG. 15C. Thus, the ion currentcompensation component 1260 enables a narrow spread of ion energies whenthe ion current is high (e.g., by compensating for effects of ioncurrent), and it also enables a width of the spread 1572, 1574 ofuniform ion energy to be controlled (e.g., when it is desirable to havea spread of ion energies).

As depicted in FIG. 15B, without ion current compensation (whenI_(I)>Ic) the voltage at the surface of the substrate, between thepositive portions of the periodic voltage function, becomes lessnegative in a ramp-like manner, which produces a broader spread 1572 ofion energies. Similarly, when ion current compensation is utilized toincrease a level of compensation current to a level that exceeds the ioncurrent (I_(I)<Ic) as depicted in FIG. 15C, the voltage at the surfaceof the substrate becomes more negative in a ramp-like manner between thepositive portions of the periodic voltage function, and a broader spread1574 of uniform ion energies is produced.

Referring back to FIG. 12, the ion current compensation component 1260may be realized as a separate accessory that may optionally be added tothe switch mode power supply 1206 and controller 1212. In otherembodiments, (e.g., as depicted in FIG. 13) the ion current compensationcomponent 1260 may share a common housing 1366 with other componentsdescribed herein (e.g., the switch-mode power supply 106, 206, 806, 1206and ion energy control 220, 820 components). In this embodiment, theperiodic voltage function provided to the plasma chamber 1204 can bereferred to as a modified periodic voltage function since it comprisesthe periodic voltage function modified by the ion current compensationfrom ion current compensation component 1260. The controller 1212 cansample a voltage at different times at an electrical node where outputsof the switch mode power supply 1206 and the ion current compensation1260 combine.

As depicted in FIG. 13, shown is an exemplary ion current compensationcomponent 1360 that includes a current source 1364 coupled to an output1336 of a switch mode supply and a current controller 1362 that iscoupled to both the current source 1364 and the output 1336. Alsodepicted in FIG. 13 is a plasma chamber 1304, and within the plasmachamber are capacitive elements C₁, C₂, and ion current I_(I). Asdepicted, C₁ represents the inherent capacitance (also referred toherein as effective capacitance) of components associated with thechamber 1304, which may include, but is not limited to, insulation, thesubstrate, substrate support, and an e-chuck, and C₂ represents sheathcapacitance and stray capacitances. In this embodiment, the periodicvoltage function provided to the plasma chamber 1304, and measurable atV₀, can be referred to as a modified periodic voltage function since itcomprises the periodic voltage function modified by the ion currentcompensation, Ic.

The sheath (also herein referred to as a plasma sheath) is a layer in aplasma near the substrate surface and possibly walls of the plasmaprocessing chamber with a high density of positive ions and thus anoverall excess of positive charge. The surface with which the sheath isin contact with typically has a preponderance of negative charge. Thesheath arises by virtue of the faster velocity of electrons thanpositive ions thus causing a greater proportion of electrons to reachthe substrate surface or walls, thus leaving the sheath depleted ofelectrons. The sheath thickness, λ_(sheath), is a function of plasmacharacteristics such as plasma density and plasma temperature.

It should be noted that because C₁ in this embodiment is an inherent(also referred to herein as effective) capacitance of componentsassociated with the chamber 1304, it is not an accessible capacitancethat is added to gain control of processing. For example, some prior artapproaches that utilize a linear amplifier couple bias power to thesubstrate with a blocking capacitor, and then utilize a monitoredvoltage across the blocking capacitor as feedback to control theirlinear amplifier. Although a capacitor could couple a switch mode powersupply to a substrate support in many of the embodiments disclosedherein, it is unnecessary to do so because feedback control using ablocking capacitor is not required in several embodiments of the presentinvention.

While referring to FIG. 13, simultaneous reference is made to FIG. 14,which is a graph depicting an exemplary voltage (e.g., the modifiedperiodic voltage function) at Vo depicted in FIG. 13. In operation, thecurrent controller 1362 monitors the voltage at Vo, and ion current iscalculated over an interval t (depicted in FIG. 14) as:

$\begin{matrix}{I_{I} = {C_{1}\frac{\mathbb{d}{V0}}{\mathbb{d}t}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

Ion current, I_(I), and inherent capacitance (also referred to aseffective capacitance), C₁, can either or both be time varying. BecauseC₁ is substantially constant for a given tool and is measurable, only Voneeds to be monitored to enable ongoing control of compensation current.As discussed above, to obtain a more mono-energetic distribution of ionenergy (e.g., as depicted in FIG. 15A) the current controller controlsthe current source 1364 so that Ic is substantially the same as I_(I)(or in the alternative, related according to Equation 2). In this way, anarrow spread of ion energies may be maintained even when the ioncurrent reaches a level that affects the voltage at the surface of thesubstrate. And in addition, if desired, the spread of the ion energy maybe controlled as depicted in FIGS. 15B and 15C so that additional ionenergies are realized at the surface of the substrate.

Also depicted in FIG. 13 is a feedback line 1370, which may be utilizedin connection with controlling an ion energy distribution. For example,the value of ΔV (also referred to herein as a voltage step or the thirdportion 1406) depicted in FIG. 14, is indicative of instantaneous ionenergy and may be used in many embodiments as part of a feedback controlloop. In one embodiment, the voltage step, ΔV, is related to ion energyaccording to Equation 4. In other embodiments, the peak-to-peak voltage,V_(PP) can be related to the instantaneous ion energy. Alternatively,the difference between the peak-to-peak voltage, V_(PP), and the productof the slope, dV₀/dt, of the fourth portion 1408 times time, t, can becorrelated to the instantaneous ion energy (e.g., V_(PP)−dV₀/dt·t).

Referring next to FIG. 16, shown is an exemplary embodiment of a currentsource 1664, which may be implemented to realize the current source 1364described with reference to FIG. 13. In this embodiment, a controllablenegative DC voltage source, in connection with a series inductor L2,function as a current source, but one of ordinary skill in the art willappreciate, in light of this specification, that a current source may berealized by other components and/or configurations.

FIG. 43 illustrates one embodiment of a method of controlling an ionenergy distribution of ions impacting a surface of a substrate. Themethod 4300 starts by applying a modified periodic voltage function 4302(see the modified periodic voltage function 4402 in FIG. 44) to asubstrate support supporting a substrate within a plasma processingchamber. The modified periodic voltage function can be controlled via atleast two ‘knobs’ such as an ion current compensation, I_(C), (see I_(C)4404 in FIG. 44) and a power supply voltage, V_(PS), (see power supplyvoltage 4406 in FIG. 44). An exemplary component for generating thepower supply voltage is the switch mode power supply 106 in FIG. 1. Inorder to help explain the power supply voltage, V_(PS), it isillustrated herein as if measured without coupling to the ion currentand ion current compensation. The modified periodic voltage function isthen sampled at a first and second value of an ion current compensation,I_(C), 4304. At least two samples of a voltage of the modified periodicvoltage function are taken for each value of the ion currentcompensation, I_(C). The sampling 4304 is performed in order to enablecalculations 4306 (or determinations) of the ion current, I_(I), and asheath capacitance, C_(sheath), 4306. Such determination may involvefinding an ion current compensation, I_(C), that if applied to thesubstrate support (or as applied to the substrate support) wouldgenerate a narrow (e.g., minimum) ion energy distribution function(IEDF) width. The calculations 4306 can also optionally includedetermining a voltage step, ΔV, (also known as a third portion of themodified periodic voltage function 1406) based on the sampling 4304 ofthe waveform of the modified periodic voltage function. The voltagestep, ΔV, can be related to the ion energy of ions reaching thesubstrate's surface. When finding the ion current, I_(I), for the firsttime, the voltage step, ΔV, can be ignored. Details of the sampling 4304and the calculations 4306 will be provided in discussions of FIG. 30 tofollow.

Once the ion current, I_(I), and sheath capacitance, C_(sheath), areknown, the method 4300 may move to the method 3100 of FIG. 31 involvingsetting and monitoring an ion energy and a shape (e.g., width) of theIEDF. For instance, FIG. 46 illustrates how a change in the power supplyvoltage can effect a change in the ion energy. In particular, amagnitude of the illustrated power supply voltage is decreased resultingin a decreased magnitude of the ion energy. Additionally, FIG. 47illustrates that given a narrow IEDF 4714, the IEDF can be widened byadjusting the ion current compensation, I_(C). Alternatively or inparallel, the method 4300 can perform various metrics as described withreference to FIGS. 32-41 that make use of the ion current, I_(I), thesheath capacitance, C_(sheath), and other aspects of the waveform of themodified periodic voltage function.

In addition to setting the ion energy and/or the IEDF width, the method4300 may adjust the modified periodic voltage function 4308 in order tomaintain the ion energy and the IEDF width. In particular, adjustment ofthe ion current compensation, I_(C), provided by an ion currentcompensation component, and adjustment of the power supply voltage maybe performed 4308. In some embodiments, the power supply voltage can becontrolled by a bus voltage, V_(bus), of the power supply (e.g., the busvoltage V_(bus) of FIG. 3). The ion current compensation, I_(C),controls the IEDF width, and the power supply voltage controls the ionenergy.

After these adjustments 4308, the modified periodic voltage function canagain be sampled 4304 and calculations of ion current, I_(I), sheathcapacitance, C_(sheath), and the voltage step, ΔV, can again beperformed 4306. If the ion current, I_(I), or the voltage step, ΔV, areother than defined values (or in the alternative, desired values), thenthe ion current compensation, I_(C), and/or the power supply voltage canbe adjusted 4308. Looping of the sampling 4304, calculating, 4306, andadjusting 4308 may occur in order to maintain the ion energy, eV, and/orthe IEDF width.

FIG. 30 illustrates another embodiment of a method of controlling an ionenergy distribution of ions impacting a surface of a substrate. In someembodiments, as discussed above, it may be desirable to achieve a narrowIEDF width (e.g., a minimum IEDF width or in the alternative, ˜6%full-width half maximum). As such, the method 3000 can provide amodified periodic voltage function to the chamber and to the substratesupport such that a constant substrate voltage, and hence sheathvoltage, exists at the surface of the substrate. This in turnaccelerates ions across the sheath at a substantially constant voltagethus enabling ions to impact the substrate with substantially the sameion energy, which in turn provides a narrow IEDF width. For instance, inFIG. 45 it can be seen that adjusting the ion current compensation,I_(C), can cause the substrate voltage, V_(sub), between pulses to havea constant, or substantially constant voltage thus causing the IEDF tonarrow.

Such a modified periodic voltage function is achieved when the ioncurrent compensation, I_(C), equals the ion current, I_(I), assuming nostray capacitances (see the last five cycles of the periodic voltagefunction (V₀) in FIG. 45). In the alternative, where stray capacitance,C_(stray), is considered, the ion current compensation, I_(C), isrelated to the ion current, I_(I), according to Equation 2:

$\begin{matrix}{I_{I} = {I_{C}\frac{C_{1}}{C_{1} + C_{stray}}}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

where, C₁, is an effective capacitance (e.g., the inherent capacitancedescribed with reference to FIGS. 3 and 13). The effective capacitance,C₁, can vary in time or be constant. For the purposes of thisdisclosure, the narrow IEDF width can exist when either I_(I)=I_(C) or,in the alternative, when Equation 2 is met. FIGS. 45-50 use thenomenclature, I_(I)=I_(C), but it should be understood that theseequalities are merely simplifications of Equation 2, and thus Equation 2could substitute for the equalities used in FIGS. 45-50. The straycapacitance, C_(stray), is a cumulative capacitance of the plasmachamber as seen by the power supply. There are eight cycles illustratedin FIG. 45.

The method 3000 can begin with an application of a modified periodicvoltage function (e.g., the modified periodic voltage function depictedin FIG. 14 or the modified periodic voltage function 4402 in FIG. 44) tothe substrate support 3002 (e.g., substrate support 108 in FIG. 1). Avoltage of the modified periodic voltage function can be sampled 3004 attwo or more times, and from this sampling, a slope dV₀/dt for at least aportion of a cycle of the modified periodic voltage function can becalculated 3006 (e.g., a slope of the portion between the pulses or thefourth portion 1408). At some point before a decision 3010, apreviously-determined value of an effective capacitance C₁ (e.g.,inherent capacitance C₁ in FIG. 13, and an inherent capacitance C10 inFIG. 3) can be accessed 3008 (e.g., from a memory or from a user input).Based on the slope, dV₀/dt, the effective capacitance, C₁, and the ioncurrent compensation, I_(C), a function ƒ (Equation 3), can be evaluatedfor each value of the ion current compensation, I_(C), as follows:

$\begin{matrix}{{f\left( I_{C} \right)} = {{\frac{\mathbb{d}V_{0}}{\mathbb{d}t} - \frac{I_{C}}{C_{1}}} = 0}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

If the function ƒ is true, then the ion current compensation, I_(C),equals the ion current, I_(I), or in the alternative, makes Equation 2true, and a narrow IEDF width has been achieved 3010 (e.g., see FIG.45). If the function ƒ is not true, then the ion current compensation,I_(C), can be adjusted 3012 further until the function ƒ is true.Another way to look at this is that the ion current compensation, I_(C),can be adjusted until it matches the ion current, I_(I), (or in thealternative, meets the relationship of Equation 2), at which point anarrow IEDF width will exist. Such an adjustment to the ion currentcompensation, Ic, and resulting narrowing of the IEDF, can be seen inFIG. 45. The ion current, I_(I), and the corresponding ion currentcompensation, Ic, can be stored (e.g., in a memory) in store operation3014. The ion current, I_(C), can vary in time, as can the effectivecapacitance, C₁.

When Equation 3 is met, ion current, I_(I), is known (either becauseI_(C)=I_(I), or because Equation 2 is true). Thus, the method 3000enables remote and non-invasive measurements of ion current, I_(I), inreal time without affecting the plasma. This leads to a number of novelmetrics such as those that will be described with reference to FIGS.32-41 (e.g., remote monitoring of plasma density and remote faultdetection of the plasma source).

While adjusting 3012 the compensation current, I_(C), the ion energywill likely be broader than a delta function and the ion energy willresemble that of either FIGS. 15B, 15C, or 44. However, once thecompensation current, I_(C), is found that meets Equation 2, the IEDFwill appear as illustrated in FIG. 15A or the right portion of FIG.45—as having a narrow IEDF width (e.g., a minimum IEDF width). This isbecause the voltage between pulses of the modified periodic voltagefunction causes a substantially constant sheath or substrate voltage,and hence ion energy, when I_(C)=I_(I) (or alternatively when Equation 2is true). In FIG. 46 the substrate voltage, 4608, includes pulsesbetween the constant voltage portions. These pulses have such a shortduration that their effect on ion energy and IEDF is negligible and thusthe substrate voltage 4608 is referred to as being substantiallyconstant.

The following provides further details about each of the method stepsillustrated in FIG. 30. In one embodiment, the modified periodic voltagefunction can have a waveform like that illustrated in FIG. 14 and caninclude a first portion (e.g., first portion 1402), a second portion(e.g., 1404), a third portion (e.g., third portion 1406), and a fourthportion (e.g., fourth portion 1408), where the third portion can have avoltage step, ΔV, and the fourth portion can have a slope, dV₀/dt. Theslope, dV₀/dt, can be positive, negative, or zero. The modified periodicvoltage function 1400 can also be described as having pulses comprisingthe first portion 1402, the second portion 1404, and the third portion1406, and a portion between the pulses (fourth portion 1408).

The modified periodic voltage function can be measured as V₀ in FIG. 3and can appear as the modified periodic voltage function 4402 in FIG.44. The modified period voltage function 4402 is produced by combiningthe power supply voltage 4406 (also known as the periodic voltagefunction) with the ion current compensation 4404. The power supplyvoltage 4406 is largely responsible for generating and shaping thepulses of the modified periodic voltage function 4402 and the ioncurrent compensation 4404 is largely responsible for generating andshaping the portion between the pulses, which is often a straight slopedvoltage. Increasing the ion current compensation, Ic, causes a decreasein a magnitude of the slope of the portion between the pulses as seen inFIG. 45. Decreasing a magnitude of the power supply voltage 4606 causesa decrease in a magnitude of the amplitude of the pulses and thepeak-to-peak voltage of the modified periodic voltage function 4602 asseen in FIG. 46.

In cases where the power supply is a switch-mode power supply, theswitching diagram 4410 of a first switch T1 and a second switch T2 canapply. For instance, the first switch T1 can be implemented as theswitch T1 in FIG. 3 and the second switch T2 can be implemented as thesecond switch T2 in FIG. 3. The two switches are illustrated as havingidentical switching times, but being 180° out of phase. In otherembodiments, the switches may have a slight phase offset such as thatillustrated in FIG. 4. When the first switch T1 is on, the power supplyvoltage is drawn to a maximum magnitude, which is a negative value inFIG. 44 since the power supply has a negative bus voltage. The secondswitch T2 is turned off during this period so that the power supplyvoltage 4406 is isolated from ground. When the switches reverse, thepower supply voltage 4406 approaches and slightly passes ground. In theillustrated embodiment, there are two pulse widths, but this is notrequired. In other embodiments, the pulse width can be identical for allcycles. In other embodiments, the pulse width can be varied or modulatedin time.

The modified periodic voltage function can be applied to the substratesupport 3002, and sampled 3004 as V₀ at a last accessible point beforethe modified periodic voltage function reaches the substrate support(e.g., between the switch mode power supply and the effectivecapacitance). The unmodified periodic voltage function (or power supplyvoltage 4406 in FIG. 44) can be sourced from a power supply such as theswitch mode power supply 1206 in FIG. 12. The ion current compensation4404 in FIG. 44 can be sourced from a current source such as the ioncurrent compensation component 1260 in FIG. 12 or 1360 in FIG. 13.

A portion of or the whole modified periodic voltage function can besampled 3004. For instance, the fourth portion (e.g., fourth portion1408) can be sampled. The sampling 3004 can be performed between thepower supply and the substrate support. For instance, in FIG. 1, thesampling 3004 can be performed between the switch mode power supply 106and the support 108. In FIG. 3, the sampling 3004 can be performedbetween the inductor L1 and the inherent capacitance C10. In oneembodiment, the sampling 3004 can be performed at V₀ between thecapacitance C3 and the inherent capacitance C10. Since the inherentcapacitance C10 and the elements representing the plasma (R2, R3, C1,and C2) are not accessible for real time measurement, the sampling 3004is typically performed to the left of the inherent capacitance C10 inFIG. 3. Although the inherent capacitance C10 typically is not measuredduring processing, it is typically a known constant, and can thereforebe set during manufacturing. At the same time, in some cases theinherent capacitance C10 can vary with time.

While only two samples of the modified periodic voltage function areneeded in some embodiments, in others, hundreds, thousands, or tens ofthousands of samples can be taken for each cycle of the modifiedperiodic voltage function. For instance, the sampling rate can begreater than 400 kHz. These sampling rates enable more accurate anddetailed monitoring of the modified periodic voltage function and itsshape. In this same vein, more detailed monitoring of the periodicvoltage function allows more accurate comparisons of the waveform:between cycles, between different process conditions, between differentprocesses, between different chambers, between different sources, etc.For instance, at these sampling rates, the first, second, third, andfourth portions 1402, 1404, 1406, 1408 of the periodic voltage functionillustrated in FIG. 14 can be distinguished, which may not be possibleat traditional sampling rates. In some embodiments, the higher samplingrates enable resolving of the voltage step, ΔV, and the slope, dV₀/dt,which are not possible in the art. In some embodiments, a portion of themodified periodic voltage function can be sampled while other portionsare not sampled.

The calculation 3006 of the slope, dV₀/dt, can be based on a pluralityof V₀ measurements taken during the time t (e.g., the fourth portion1408). For instance, a linear fit can be performed to fit a line to theV₀ values where the slope of the line gives the slope, dV₀/dt. Inanother instance, the V₀ values at the beginning and end of time t(e.g., the fourth portion 1408) in FIG. 14 can be ascertained and a linecan be fit between these two points with the slope of the line given asdV₀/dt. These are just two of numerous ways that the slope, dV₀/dt, ofthe portion between the pulses can be calculated.

The decision 3010 can be part of an iterative loop used to tune the IEDFto a narrow width (e.g., a minimum width, or in the alternative, 6%full-width half maximum). Equation 3 only holds true where the ioncurrent compensation, Ic, is equal to the ion current, I_(I) (or in thealternative, is related to I_(I) according to Equation 2), which onlyoccurs where there is a constant substrate voltage and thus a constantand substantially singular ion energy (a narrow IEDF width). A constantsubstrate voltage 4608 (V_(sub)) can be seen in FIG. 46. Thus, eitherion current, I_(I), or alternatively ion current compensation, Ic, canbe used in Equation 3.

Alternatively, two values along the fourth portion 1408 (also referredto as the portion between the pulses) can be sampled for a first cycleand a second cycle and a first and second slope can be determined foreach cycle, respectively. From these two slopes, an ion currentcompensation, Ic, can be determined which is expected to make Equation 3true for a third, but not-yet-measured, slope. Thus, an ion current,I_(I), can be estimated that is predicted to correspond to a narrow IEDFwidth. These are just two of the many ways that a narrow IEDF width canbe determined, and a corresponding ion current compensation, Ic, and/ora corresponding ion current, I_(I), can be found.

The adjustment to the ion current compensation, Ic, 3012 can involveeither an increase or a decrease in the ion current compensation, Ic,and there is no limitation on the step size for each adjustment. In someembodiments, a sign of the function ƒ in Equation 3 can be used todetermine whether to increase or decrease the ion current compensation.If the sign is negative, then the ion current compensation, Ic, can bedecreased, while a positive sign can indicate the need to increase theion current compensation, Ic.

Once an ion current compensation, Ic, has been identified that equalsthe ion current, I_(I) (or in the alternative, is related theretoaccording to Equation 2), the method 3000 can advance to further setpoint operations (see FIG. 31) or remote chamber and source monitoringoperations (see FIGS. 32-41). The further set point operations caninclude setting the ion energy (see also FIG. 46) and the distributionof ion energy or IEDF width (see also FIG. 47). The source and chambermonitoring can include monitoring plasma density, source supplyanomalies, plasma arcing, and others.

Furthermore, the method 3000 can optionally loop back to the sampling3004 in order to continuously (or in the alternative, periodically)update the ion current compensation, Ic. For instance, the sampling3004, calculation 3006, the decision 3010, and the adjusting 3012 canperiodically be performed given a current ion current compensation, Ic,in order to ensure that Equation 3 continues to be met. At the sametime, if the ion current compensation, Ic, that meets Equation 3 isupdated, then the ion current, I_(I), can also be updated and theupdated value can be stored 3014.

While the method 3000 can find and set the ion current compensation, Ic,so as to equal the ion current, I_(I), or in the alternative, to meetEquation 2, a value for the ion current compensation, Ic, needed toachieve a narrow IEDF width can be determined without (or in thealternative, before) setting the ion current, I_(C), to that value. Forinstance, by applying a first ion current compensation, Ic₁, for a firstcycle and measuring a first slope, dV₀₁/dt, of the voltage between thepulses, and by applying a second ion current compensation, Ic₂, for asecond cycle and measuring a second slope, dV₀₂/dt, of the voltagebetween the pulses, a third slope, dV₀₃/dt, associated with a third ioncurrent compensation, Ic₃, can be determined at which Equation 3 isexpected to be true. The third ion current compensation, Ic₃, can be onethat if applied would result in a narrow IEDF width. Hence, the ioncurrent compensation, Ic, that meets Equation 3 and thus corresponds toion current, I_(I), can be determined with only a single adjustment ofthe ion current compensation. The method 3000 can then move on to themethods described in FIG. 31 and/or FIGS. 32-41 without ever setting theion current, I_(C), to a value needed to achieve the narrow IEDF width.Such an embodiment may be carried out in order to increase tuningspeeds.

FIG. 31 illustrates methods for setting the IEDF width and the ionenergy. The method originates from the method 3000 illustrated in FIG.30, and can take either of the left path 3100 (also referred to as anIEDF branch) or the right path 3101 (also referred to as an ion energybranch), which entail setting of the IEDF width and the ion energy,respectively. Ion energy, eV, is proportional to a voltage step, ΔV, orthe third portion 1406 of the modified periodic voltage function 1400 ofFIG. 14. The relationship between ion energy, eV, and the voltage step,ΔV, can be written as Equation 4:

$\begin{matrix}{{e\; V} = {\Delta\; V\frac{c_{1}}{c_{2} + c_{1}}}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

where C₁ is the effective capacitance (e.g., chuck capacitance; inherentcapacitance, C10, in FIG. 3; or inherent capacitance, C1, in FIG. 13),and C₂ is a sheath capacitance (e.g., the sheath capacitance C4 in FIG.3 or the sheath capacitance C2 in FIG. 13). The sheath capacitance, C₂,may include stray capacitances and depends on the ion current, I_(I).The voltage step, ΔV, can be measured as a change in voltage between thesecond portion 1404 and the fourth portion 1408 of the modified periodicvoltage function 1400. By controlling and monitoring the voltage step,ΔV, (which is a function of a power supply voltage or a bus voltage suchas bus voltage, V_(bus) in FIG. 3), ion energy, eV, can be controlledand known.

At the same time, the IEDF width can be approximated according toEquation 5:

$\begin{matrix}{{{IEDF}\mspace{14mu}{width}} = {V_{PP} - {\Delta\; V} - \frac{It}{C}}} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$

where I is I_(I) where C is C_(series), or I is I_(C) where C isC_(effective). Time, t, is the time between pulses, V_(PP), is thepeak-to-peak voltage, and ΔV is the voltage step.

Additionally, sheath capacitance, C₂, can be used in a variety ofcalculations and monitoring operations. For instance, the Debye sheathdistance, λ_(sheath), can be estimated as follows:

$\begin{matrix}{\lambda_{sheath} = \frac{\varepsilon\; A}{C_{2}}} & \left( {{Equation}\mspace{14mu} 6} \right)\end{matrix}$

where ε is vacuum permittivity and A is an area of the substrate (or inan alternative, a surface area of the substrate support). In some highvoltage applications, Equation 6 is written as equation 7:

$\begin{matrix}{\lambda_{sheath} = {\sqrt{\frac{T_{e} \cdot \varepsilon_{0}}{n_{e}q}} \cdot \left( {\frac{V}{2}T_{e}} \right)^{.75}}} & \left( {{Equation}\mspace{14mu} 7} \right)\end{matrix}$

Additionally, an e-field in the sheath can be estimated as a function ofthe sheath capacitance, C₂, the sheath distance, λ_(sheath), and the ionenergy, eV. Sheath capacitance, C₂, along with the ion current, I_(I),can also be used to determine plasma density, n_(e), from Equation 8where saturation current, I_(sat), is linearly related to thecompensation current, I_(C), for singly ionized plasma.

$\begin{matrix}{I_{sat} = {{\sum{n_{i}q_{i}\sqrt{\frac{{kT}_{e}}{m_{i}}}A}} \approx {n_{e}q\sqrt{\frac{{kT}_{e}}{\left\langle m \right\rangle}}A}}} & \left( {{Equation}\mspace{14mu} 8} \right)\end{matrix}$

An effective mass of ions at the substrate surface can be calculatedusing the sheath capacitance, C₂ and the saturation current, I_(sat).Plasma density, n_(e), electric field in the sheath, ion energy, eV,effective mass of ions, and a DC potential of the substrate, V_(DC), arefundamental plasma parameters that are typically only monitored viaindirect means in the art. This disclosure enables direct measurementsof these parameters thus enabling more accurate monitoring of plasmacharacteristics in real time.

As seen in Equation 4, the sheath capacitance, C₂, can also be used tomonitor and control the ion energy, eV, as illustrated in the ion energybranch 3101 of FIG. 31. The ion energy branch 3101 starts by receiving auser selection of ion energy 3102. The ion energy branch 3101 can thenset an initial power supply voltage for the switch-mode power supplythat supplies the periodic voltage function 3104. At some point before asample periodic voltage operation 3108, the ion current can also beaccessed 3106 (e.g., accessed from a memory). The periodic voltage canbe sampled 3108 and a measurement of the third portion of the modifiedperiodic voltage function can be measured 3110. Ion energy, I_(I), canbe calculated from the voltage step, ΔV, (also referred to as the thirdportion (e.g., third portion 1406)) of the modified periodic voltagefunction 3112. The ion energy branch 3101 can then determine whether theion energy equals the defined ion energy 3114, and if so, the ion energyis at the desired set point and the ion energy branch 3101 can come toan end. If the ion energy is not equal to the defined ion energy, thenthe ion energy branch 3101 can adjust the power supply voltage 3116, andagain sample the periodic voltage 3108. The ion energy branch 3101 canthen loop through the sampling 3108, measuring 3110, calculating 3112,decision 3114, and the setting 3116 until the ion energy equals thedefined ion energy.

The method for monitoring and controlling the IEDF width is illustratedin the IEDF branch 3100 of FIG. 31. The IEDF branch 3100 includesreceiving a user selection of an IEDF width 3150 and sampling a currentIEDF width 3152. A decision 3154 then determines whether the definedIEDF width equals the current IEDF width, and if the decision 3152 ismet, then the IEDF width is as desired (or defined), and the IEDF branch3100 can come to an end. However, if the current IEDF width does notequal the defined IEDF width, then the ion current compensation, Ic, canbe adjusted 3156. This determination 3154 and the adjustment 3156 cancontinue in a looping manner until the current IEDF width equals thedefined IEDF width.

In some embodiments, the IEDF branch 3100 can also be implemented tosecure a desired IEDF shape. Various IEDF shapes can be generated andeach can be associated with a different ion energy and IEDF width. Forinstance, a first IEDF shape may be a delta function while a second IEDFshape may be a square function. Other IEDF shapes may be cupped.Examples of various IEDF shapes can be seen in FIG. 11.

With knowledge of the ion current, I_(I), and the voltage step, ΔV,Equation 4 can be solved for ion energy, eV. The voltage step, ΔV, canbe controlled by changing the power supply voltage which in turn causesthe voltage step, ΔV, to change. A larger power supply voltage causes anincrease in the voltage step, ΔV, and a decrease in the power supplyvoltage causes a decrease in the voltage step, ΔV. In other words,increasing the power supply voltage results in a larger ion energy, eV.

Furthermore, since the above systems and methods operate on acontinuously varying feedback loop, the desired (or defined) ion energyand IEDF width can be maintained despite changes in the plasma due tovariations or intentional adjustments to the plasma source or chamberconditions.

Although FIGS. 30-41 have been described in terms of a single ionenergy, one of skill in the art will recognize that these methods ofgenerating and monitoring a desired (or defined) IEDF width (or IEDFshape) and ion energy can be further utilized to produce and monitor twoor more ion energies, each having its own IEDF width (or IEDF shape).For instance, by providing a first power supply voltage, V_(PS), in afirst, third, and fifth cycles, and a second power supply voltage in asecond, fourth, and sixth cycles, two distinct and narrow ion energiescan be achieved for ions reaching the surface of the substrate (e.g.,FIG. 42A). Using three different power supply voltages results in threedifferent ion energies (e.g., FIG. 42B). By varying a time during whicheach of multiple power supply voltages is applied, or the number ofcycles during which each power supply voltage level is applied, the ionflux of different ion energies can be controlled (e.g., FIG. 42C).

The above discussion has shown how combining a periodic voltage functionprovided by a power supply with an ion current compensation provided byan ion current compensation component, can be used to control an ionenergy and IEDF width and/or IEDF shape of ions reaching a surface of asubstrate during plasma processing.

Some of the heretofore mentioned controls are enabled by using somecombination of the following: (1) a fixed waveform (consecutive cyclesof the waveform are the same); (2) a waveform having at least twoportions that are proportional to an ion energy and an IEDF (e.g., thethird and fourth portions 1406 and 1408 illustrated in FIG. 14); and (3)a high sampling rate (e.g., 125 MHz) that enables accurate monitoring ofthe distinct features of the waveform. For instance, where the priorart, such as linear amplifiers, sends a waveform to the substrate thatis similar to the modified periodic voltage function, undesiredvariations between cycles make it difficult to use those prior artwaveforms to characterize the ion energy or IEDF width (or IEDF shape).

Where linear amplifiers have been used to bias a substrate support, theneed to sample at a high rate has not been seen since the waveform isnot consistent from cycle to cycle and thus resolving features of thewaveform (e.g., a slope of a portion between pulses) typically would notprovide useful information. Such useful information does arise when afixed waveform is used, as seen in this and related disclosures.

The herein disclosed fixed waveform and the high sampling rate furtherlead to more accurate statistical observations being possible. Becauseof this increased accuracy, operating and processing characteristics ofthe plasma source and the plasma in the chamber can be monitored viamonitoring various characteristics of the modified periodic voltagefunction. For instance, measurements of the modified periodic voltagefunction enable remote monitoring of sheath capacitance and ion current,and can be monitored without knowledge of the chamber process or otherchamber details. A number of examples follow to illustrate just some ofthe multitude of ways that the heretofore mentioned systems and methodscan be used for non-invasive monitoring and fault detection of thesource and chamber.

As an example of monitoring, and with reference to FIG. 14, the DCoffset of the waveform 1400 can represent a health of the plasma source(hereinafter referred to as the “source”). In another, a slope of a topportion 1404 (the second portion) of a pulse of the modified periodicvoltage function can be correlated to damping effects within the source.The standard deviation of the slope of the top portion 1404 fromhorizontal (illustrated as having a slope equal to 0) is another way tomonitor source health based on an aspect of the waveform 1400. Anotheraspect involves measuring a standard deviation of sampled V₀ pointsalong the fourth portion 1408 of the modified periodic voltage functionand correlating the standard deviation to chamber ringing. For instance,where this standard deviation is monitored among consecutive pulses, andthe standard deviation increases over time, this may indicate that thereis ringing in the chamber, for instance in the e-chuck. Ringing can be asign of poor electrical connections to, or in, the chamber or ofadditional unwanted inductance or capacitance.

FIG. 32 illustrates two modified periodic voltage functions delivered tothe substrate support according to one embodiment of this disclosure.When compared, the two modified periodic voltage functions can be usedfor chamber matching or in situ anomaly or fault detection. Forinstance, one of the two modified periodic voltage functions can be areference waveform and the second can be taken from a plasma processingchamber during calibration. Differences between the two modifiedperiodic voltage functions (e.g., differences in peak-to-peak voltage,V_(PP)) can be used to calibrate the plasma processing chamber.Alternatively, the second modified periodic voltage function can becompared to the reference waveform during processing and any difference(e.g., shifts) in waveform characteristics can be indicative of a fault(e.g., a difference in the slope of a fourth portion 3202 of themodified periodic voltage functions).

FIG. 33 illustrates an ion current waveform that can indicate plasmasource instability and changes in the plasma density. Fluctuations inion current, I_(I), such as that illustrated in FIG. 33, can be analyzedto identify faults and anomalies in the system. For instance, theperiodic fluctuations in FIG. 33 may indicate a low-frequencyinstability in the plasma source (e.g., plasma power supply 102). Suchfluctuations in ion current, I_(I), can also indicate cyclical changesin plasma density. This indicator and the possible faults or anomaliesthat it may indicate are just one of many ways that remote monitoring ofthe ion current, I_(I), can be used to particular advantage.

FIG. 34 illustrates an ion current, I_(I), of a modified periodicvoltage function having a non-cyclical shape. This embodiment of an ioncurrent, I_(I), can indicate non-cyclical fluctuations such as plasmainstability and changes in plasma density. Such a fluctuation may alsoindicate various plasma instabilities such as arcing, formation ofparasitic plasma, or drift in plasma density.

FIG. 35 illustrates a modified periodic voltage function that canindicate faults within the bias supply. A top portion (also referred toherein as a second portion) of the third illustrated cycle showsanomalous behavior that may be indicative of ringing in the bias supply(e.g., power supply 1206 in FIG. 12). This ringing may be an indicationof a fault within the bias supply. Further analysis of the ringing mayidentify characteristics that help to identify the fault within thepower system.

FIG. 36 illustrates a modified periodic voltage function that can beindicative of a dynamic (or nonlinear) change in a capacitance of thesystem. For instance, a stray capacitance that nonlinearly depends onvoltage could result in such a modified periodic voltage function. Inanother example, plasma breakdown or a fault in the chuck could alsoresult in such a modified periodic voltage function. In each of thethree illustrated cycles a nonlinearity in the fourth portion 3602 ofeach cycle can be indicative of a dynamic change in the systemcapacitance. For instance, the nonlinearities can indicate a change inthe sheath capacitance since other components of system capacitance arelargely fixed.

FIG. 37 illustrates a modified periodic voltage function that may beindicative of changes in plasma density. The illustrated modifiedperiodic voltage function shows monotonic shifts in the slope dV₀/dt,which can indicate a change in plasma density. These monotonic shiftscan provide a direct indication of an anticipated event, such as aprocess etch end point. In other embodiments, these monotonic shifts canindicate a fault in the process where no anticipated event exists.

FIG. 38 illustrates a sampling of ion current for different processruns, where drift in the ion current can indicate system drift. Eachdata point can represent an ion current for a given run, where theacceptable limit is a user-defined or automated limit which defines anacceptable ion current. Drift in the ion current, which gradually pushesthe ion current above the acceptable limit can indicate that substratedamage is possible. This type of monitoring can also be combined withany number of other traditional monitors, such as optical omission,thickness measurement, etc. These traditional types of monitors inaddition to monitoring ion current drift can enhance existing monitoringand statistical control.

FIG. 39 illustrates a sampling of ion current for different processparameters. In this illustration ion current can be used as a figure ofmerit to differentiate different processes and different processcharacteristics. Such data can be used in the development of plasmarecipes and processes. For instance eleven process conditions could betested resulting in the eleven illustrated ion current data points, andthe process resulting in a preferred ion current can be selected as anideal process, or in the alternative as a preferred process. Forinstance, the lowest ion current may be selected as the ideal process,and thereafter the ion current associated with the preferred process canbe used as a metric to judge whether a process is being carried out withthe preferred process condition(s). This figure of merit can be used inaddition to or as an alternative to similar traditional meritcharacteristics such as rate, selectivity, and profile angle, to name afew non-limiting examples.

FIG. 40 illustrates two modified periodic voltage functions monitoredwithout a plasma in the chamber. These two modified periodic voltagefunctions can be compared and used to characterize the plasma chamber.In an embodiment the first modified periodic voltage function can be areference waveform while the second modified periodic voltage functioncan be a currently-monitored waveform. These waveforms can be takenwithout a plasma in the processing chamber, for instance after a chamberclean or preventative maintenance, and therefore the second waveform canbe used to provide validation of an electrical state of the chamberprior to release of the chamber into (or back into) production.

FIG. 41 illustrates two modified periodic voltage functions that can beused to validate a plasma process. The first modified periodic voltagefunction can be a reference waveform while the second modified periodicvoltage function can be a currently monitored waveform. The currentlymonitored waveform can be compared to the reference waveform and anydifferences can indicate parasitic and/or non-capacitive impedanceissues that are otherwise not detectable using traditional monitoringmethods. For instance, the ringing seen on the waveform of FIG. 35 maybe detected and could represent ringing in the power supply.

Any of the metrics illustrated in FIGS. 32-41 can be monitored while themethod 3000 loops in order to update the ion current compensation, Ic,ion current, I_(I), and/or the sheath capacitance, C_(sheath). Forinstance, after each ion current, I_(I), sample is taken in FIG. 38, themethod 3000 can loop back to the sampling 3004 in order to determine anupdated ion current, I_(I). In another example, as a result of amonitoring operation, a correction to the ion current, I_(I), ionenergy, eV, or the IEDF width may be desired. A corresponding correctioncan be made and the method 3000 can loop back to the sampling 3004 tofind a new ion current compensation, Ic, that meets Equation 3.

One of skill in the art will recognize that the methods illustrated inFIGS. 30, 31, and 43 do not require any particular or described order ofoperation, nor are they limited to any order illustrated by or impliedin the figures. For instance, metrics (FIGS. 32-41) can be monitoredbefore, during, or after setting and monitoring the IEDF width and/orthe ion energy, eV.

FIG. 44 illustrates various waveforms at different points in the systemsherein disclosed. Given the illustrated switching pattern 4410 forswitching components of a switch mode power supply, power supplyvoltage, V_(PS), 4406 (also referred to herein as a periodic voltagefunction), ion current compensation, Ic, 4404, modified periodic voltagefunction 4402, and substrate voltage, V_(sub), 4412, the IEDF has theillustrated width 4414 (which may not be drawn to scale) or IEDF shape4414. This width is wider than what this disclosure has referred to as a“narrow width.” As seen, when the ion current compensation, Ic, 4404 isgreater than the ion current, I_(I), the substrate voltage, V_(sub),4412 is not constant. The IEDF width 4414 is proportional to a voltagedifference of the sloped portion between pulses of the substratevoltage, V_(sub), 4412.

Given this non-narrow IEDF width 4414, the methods herein disclosed callfor the ion current compensation, Ic, to be adjusted until I_(C)=I_(I)(or in the alternative are related according to Equation 2). FIG. 45illustrates the effects of making a final incremental change in ioncurrent compensation, Ic, in order to match it to ion current I_(I).When I_(C)=I_(I) the substrate voltage, V_(sub), 4512 becomessubstantially constant, and the IEDF width 4514 goes from non-narrow tonarrow.

Once the narrow IEDF has been achieved, one can adjust the ion energy toa desired or defined value as illustrated in FIG. 46. Here, a magnitudeof the power supply voltage (or in the alternative a bus voltage,V_(bus), of a switch-mode power supply) is decreased (e.g., a maximumnegative amplitude of the power supply voltage 4606 pulses is reduced).As a result, ΔV₁ decreases to ΔV₂ as does the peak-to-peak voltage, fromV_(PP1) to V_(PP2). A magnitude of the substantially constant substratevoltage, V_(sub), 4608 consequently decreases, thus decreasing amagnitude of the ion energy from 4615 to 4614 while maintaining thenarrow IEDF width.

Whether the ion energy is adjusted or not, the IEDF width can be widenedafter the narrow IEDF width is achieved as shown in FIG. 47. Here, givenI_(I)=I_(C) (or in the alternative, Equation 2 giving the relationbetween I_(I) and I_(C)), I_(C) can be adjusted thus changing a slope ofthe portion between pulses of the modified periodic voltage function4702. As a result of ion current compensation, Ic, and ion current,I_(I), being not equal, the substrate voltage moves from substantiallyconstant to non-constant. A further result is that the IEDF width 4714expands from the narrow IEDF 4714 to a non-narrow IEDF 4702. The morethat I_(C) is adjusted away from I_(I), the greater the IEDF 4714 width.

FIG. 48 illustrates one pattern of the power supply voltage that can beused to achieve more than one ion energy level where each ion energylevel has a narrow IEDF 4814 width. A magnitude of the power supplyvoltage 4806 alternates each cycle. This results in an alternating ΔVand peak-to-peak voltage for each cycle of the modified periodic voltagefunction 4802. The substrate voltage 4812 in turn has two substantiallyconstant voltages that alternate between pulses of the substratevoltage. This results in two different ion energies each having a narrowIEDF 4814 width.

FIG. 49 illustrates another pattern of the power supply voltage that canbe used to achieve more than one ion energy level where each ion energylevel has a narrow IEDF 4914 width. Here, the power supply voltage 4906alternates between two different magnitudes but does so for two cyclesat a time before alternating. As seen, the average ion energies are thesame as if V_(PS) 4906 were alternated every cycle. This shows just oneexample of how various other patterns of the V_(PS) 4906 can be used toachieve the same ion energies.

FIG. 50 illustrates one combination of power supply voltages, V_(PS),5006 and ion current compensation, Ic, 5004 that can be used to create adefined IEDF 5014. Here, alternating power supply voltages 5006 resultin two different ion energies. Additionally, by adjusting the ioncurrent compensation 5004 away from the ion current, I_(I), the IEDF5014 width for each ion energy can be expanded. If the ion energies areclose enough, as they are in the illustrated embodiment, then the IEDF5014 for both ion energies will overlap resulting in one large IEDF5014. Other variations are also possible, but this example is meant toshow how combinations of adjustments to the V_(PS) 5006 and the I_(C)5004 can be used to achieve defined ion energies and defined IEDFs 5014.

Referring next to FIGS. 17A and 17B, shown are block diagrams depictingother embodiments of the present invention. As shown, the substratesupport 1708 in these embodiments includes an electrostatic chuck 1782,and an electrostatic chuck supply 1780 is utilized to apply power to theelectrostatic chuck 1782. In some variations, as depicted in FIG. 17A,the electrostatic chuck supply 1780 is positioned to apply powerdirectly to the substrate support 1708, and in other variations, theelectrostatic chuck supply 1780 is positioned to apply power inconnection with the switch mode power supply. It should be noted thatserial chucking can be carried by either a separate supply or by use ofthe controller to effect a net DC chucking function. In this DC-coupled(e.g., no blocking capacitor), series chucking function, the undesiredinterference with other RF sources can be minimized.

Shown in FIG. 18 is a block diagram depicting yet another embodiment ofthe present invention in which a plasma power supply 1884 that generallyfunctions to generate plasma density is also configured to drive thesubstrate support 1808 alongside the switch mode power supply 1806 andelectrostatic chuck supply 1880. In this implementation, each of theplasma power supply 1884, the electrostatic chuck supply 1880, and theswitch mode power supply 1806 may reside in separate assemblies, or twoor more of the supplies 1806, 1880, 1884 may be architected to reside inthe same physical assembly. Beneficially, the embodiment depicted inFIG. 18 enables a top electrode 1886 (e.g., shower head) to beelectrically grounded so as to obtain electrical symmetry and reducedlevel of damage due to fewer arcing events.

Referring to FIG. 19, shown is a block diagram depicting still anotherembodiment of the present invention. As depicted, the switch mode powersupply 1906 in this embodiment is configured to apply power to thesubstrate support and the chamber 1904 so as to both bias the substrateand ignite (and sustain) the plasma without the need for an additionalplasma power supply (e.g., without the plasma power supply 102, 202,1202, 1702, 1884). For example, the switch-mode power supply 1806 may beoperated at a duty cycle that is sufficient to ignite and sustain theplasma while providing a bias to the substrate support.

Referring next to FIG. 20, it is a block diagram depicting inputparameters and control outputs of a control portion that may be utilizedin connection with the embodiments described with reference to FIGS.1-19. The depiction of the control portion is intended to provide asimplified depiction of exemplary control inputs and outputs that may beutilized in connection with the embodiments discussed herein—it is notintended to a be hardware diagram. In actual implementation, thedepicted control portion may be distributed among several discretecomponents that may be realized by hardware, software, firmware, or acombination thereof.

With reference to the embodiments previously discussed herein, thecontroller depicted in FIG. 20 may provide the functionality of one ormore of the controller 112 described with reference to FIG. 1; thecontroller 212 and ion energy control 220 components described withreference to FIG. 2; the controller 812 and ion energy control portion820 described with reference to FIG. 8; the ion current compensationcomponent 1260 described with reference to FIG. 12; the currentcontroller 1362 described with reference to FIG. 13; the Icc controldepicted in FIG. 16, controllers 1712A, 1712B depicted in FIGS. 17A and17B, respectively; and controllers 1812, 1912 depicted in FIGS. 18 and19, respectively.

As shown, the parameters that may be utilized as inputs to the controlportion include dVo/dt and ΔV, which are described in more detail withreference to FIGS. 13 and 14. As discussed, dVo/dt may be utilized to inconnection with an ion-energy-distribution-spread input ΔE to provide acontrol signal Icc, which controls a width of the ion energydistribution spread as described with reference to FIGS. 12, 13, 14,15A-C, and FIG. 16. In addition, an ion energy control input (Ei) inconnection with optional feedback ΔV may be utilized to generate an ionenergy control signal (e.g., that affects Vbus depicted in FIG. 3) toeffectuate a desired (or defined) ion energy distribution as describedin more detail with reference to FIGS. 1-11. And another parameter thatmay be utilized in connection with many e-chucking embodiments is a DCoffset input, which provides electrostatic force to hold the wafer tothe chuck for efficient thermal control.

FIG. 21 illustrates a plasma processing system 2100 according to anembodiment of this disclosure. The system 2100 includes a plasmaprocessing chamber 2102 enclosing a plasma 2104 for etching a topsurface 2118 of a substrate 2106 (and other plasma processes). Theplasma is generated by a plasma source 2112 (e.g., in-situ or remote orprojected) powered by a plasma power supply 2122. A plasma sheathvoltage V_(sheath) measured between the plasma 2104 and the top surface2118 of the substrate 2106 accelerates ions from the plasma 2104 acrossa plasma sheath 2115, causing the accelerated ions to impact a topsurface 2118 of a substrate 2106 and etch the substrate 2106 (orportions of the substrate 2106 not protected by photoresist). The plasma2104 is at a plasma potential V₃ relative to ground (e.g., the plasmaprocessing chamber 2102 walls). The substrate 2106 has a bottom surface2120 that is electrostatically held to a support 2108 via anelectrostatic chuck 2111 and a chucking potential V_(chuck) between atop surface 2121 of the electrostatic chuck 2111 and the substrate 2106.The substrate 2106 is dielectric and therefore can have a firstpotential V₁ at the top surface 2118 and a second potential V₂ at thebottom surface 2120. The top surface of the electrostatic chuck 2121 isin contact with the bottom surface 2120 of the substrate, and thus thesetwo surfaces 2120, 2121 are at the same potential, V₂. The firstpotential V₁, the chucking potential V_(chuck), and the second potentialV₂, are controlled via an AC waveform with a DC bias or offset generatedby a switch mode power supply 2130 and provided to the electrostaticchuck 2111 via a first conductor 2124. Optionally, the AC waveform isprovided via the first conductor 2124, and the DC waveform is providedvia an optional second conductor 2125. The AC and DC output of theswitch mode power supply 2130 can be controlled via a controller 2132,which is also configured to control various aspects of the switch modepower supply 2130.

Ion energy and ion energy distribution are a function of the firstpotential V₁. The switch mode power supply 2130 provides an AC waveformtailored to effect a desired first potential V₁ known to generate adesired (or defined) ion energy and ion energy distribution. The ACwaveform can be RF and have a non-sinusoidal waveform such as thatillustrated in FIGS. 5, 6, 11, 14, 15 a, 15 b, and 15 c. The firstpotential V₁ can be proportional to the change in voltage ΔV illustratedin FIG. 14. The first potential V₁ is also equal to the plasma voltageV₃ minus the plasma sheath voltage V_(sheath). But since the plasmavoltage V₃ is often small (e.g., less than 20 V) compared to the plasmasheath voltage V_(sheath) (e.g., 50 V-2000 V), the first potential V₁and the plasma sheath voltage V_(sheath) are approximately equal and forpurposes of implementation can be treated as being equal. Thus, sincethe plasma sheath voltage V_(sheath) dictates ion energies, the firstpotential V₁ is proportional to ion energy distribution. By maintaininga constant first potential V₁, the plasma sheath voltage V_(sheath) isconstant, and thus substantially all ions are accelerated via the sameenergy, and hence a narrow ion energy distribution is achieved. Theplasma voltage V₃ results from energy imparted to the plasma 2104 viathe plasma source 2112.

The first potential V₁ at the top surface 2118 of the substrate 2106 isformed via a combination of capacitive charging from the electrostaticchuck 2111 and charge buildup from electrons and ions passing throughthe sheath 2115. The AC waveform from the switch mode power supply 2130is tailored to offset the effects of ion and electron transfer throughthe sheath 2115 and the resulting charge buildup at the top surface 2118of the substrate 2106 such that the first potential V₁ remainssubstantially constant.

The chucking force that holds the substrate 2106 to the electrostaticchuck 2111 is a function of the chucking potential V_(chuck). The switchmode power supply 2130 provides a DC bias, or DC offset, to the ACwaveform, so that the second potential V₂ is at a different potentialthan the first potential V₁. This potential difference causes thechucking voltage V_(chuck). The chucking voltage V_(chuck) can bemeasured from the top surface 2221 of the electrostatic chuck 2111 to areference layer inside the substrate 2106, where the reference layerincludes any elevation inside the substrate except a bottom surface 2120of the substrate 2106 (the exact location within the substrate 2106 ofthe reference layer can vary). Thus, chucking is controlled by and isproportional to the second potential V₂.

In an embodiment, the second potential V₂ is equal to the DC offset ofthe switch mode power supply 2130 modified by the AC waveform (in otherwords an AC waveform with a DC offset where the DC offset is greaterthan a peak-to-peak voltage of the AC waveform). The DC offset may besubstantially larger than the AC waveform, such that the DC component ofthe switch mode power supply 2130 output dominates the second potentialV₂ and the AC component can be neglected or ignored.

The potential within the substrate 2106 varies between the first andsecond potentials V₁, V₂. The chucking potential V_(chuck) can bepositive or negative (e.g., V₁>V₂ or V₁<V₂) since the coulombicattractive force between the substrate 2106 and the electrostatic chuck2111 exists regardless of the chucking potential V_(chuck) polarity.

The switch mode power supply 2130 in conjunction with the controller2132 can monitor various voltages deterministically and without sensors.In particular, the ion energy (e.g., mean energy and ion energydistribution) is deterministically monitored based on parameters of theAC waveform (e.g., slope and step). For instance, the plasma voltage V₃,ion energy, and ion energy distribution are proportional to parametersof the AC waveform produced by the switch mode power supply 2130. Inparticular the ΔV of the falling edge of the AC waveform (see forexample FIG. 14), is proportional to the first potential V₁, and thus tothe ion energy. By keeping the first potential V₁ constant, the ionenergy distribution can be kept narrow.

Although the first potential V₁ cannot be directly measured and thecorrelation between the switch mode power supply output and the firstvoltage V₁ may vary based on the capacitance of the substrate 2106 andprocessing parameters, a constant of proportionality between ΔV and thefirst potential V₁ can be empirically determined after a shortprocessing time has elapsed. For instance, where the falling edge ΔV ofthe AC waveform is 50 V, and the constant of proportionality isempirically found to be 2 for the given substrate and process, the firstpotential V₁ can be expected to be 100 V. A proportionality between thestep voltage, ΔV, and the first potential V₁ (and thus also ion energy,eV) is described by Equation 4. Thus, the first potential V₁, along withion energy, and ion energy distribution can be determined based onknowledge of the AC waveform of the switch mode power supply without anysensors inside the plasma processing chamber 2102. Additionally, theswitch mode power supply 2130 in conjunction with the controller 2132can monitor when and if chucking is taking place (e.g., whether thesubstrate 2106 is being held to the electrostatic chuck 2111 via thechucking potential V_(chuck)).

Dechucking is performed by eliminating or decreasing the chuckingpotential V_(chuck). This can be done by setting the second potential V₂equal to the first potential V₁. In other words, the DC offset and theAC waveform can be adjusted in order to cause the chucking voltageV_(chuck) to approach 0 V. Compared to conventional dechucking methods,the system 2100 achieves faster dechucking and thus greater throughputsince both the DC offset and the AC waveform can be adjusted to achievedechucking. Also, when the DC and AC power supplies are in the switchmode power supply 2130, their circuitry is more unified, closertogether, can be controlled via a single controller 2132 (as compared totypical parallel arrangements of DC and AC power supplies), and changeoutput faster. The speed of dechucking enabled by the embodiments hereindisclosed also enables dechucking after the plasma 2104 is extinguished,or at least after power from the plasma source 2112 has been turned off.

The plasma source 2112 can take a variety of forms. For instance, in anembodiment, the plasma source 2112 includes an electrode inside theplasma processing chamber 2102 that establishes an RF field within thechamber 2102 that both ignites and sustains the plasma 2104. In anotherembodiment, the plasma source 2112 includes a remote projected plasmasource that remotely generates an ionizing electromagnetic field,projects or extends the ionizing electromagnetic field into theprocessing chamber 2102, and both ignites and sustains the plasma 2104within the plasma processing chamber using the ionizing electromagneticfield. Yet, the remote projected plasma source also includes a fieldtransfer portion (e.g., a conductive tube) that the ionizingelectromagnetic field passes through en route to the plasma processingchamber 2102, during which time the ionizing electromagnetic field isattenuated such that the field strength within the plasma processingchamber 2102 is only a tenth or a hundred or a thousandth or an evensmaller portion of the field strength when the field is first generatedin the remote projected plasma source. The plasma source 2112 is notdrawn to scale.

The switch mode power supply 2130 can float and thus can be biased atany DC offset by a DC power source (not illustrated) connected in seriesbetween ground and the switch mode power supply 2130. The switch modepower supply 2130 can provide an AC waveform with a DC offset either viaAC and DC power sources internal to the switch mode power supply 2130(see for example FIGS. 22, 23, 26), or via an AC power source internalto the switch mode power supply 2130 and a DC power supply external tothe switch mode power supply 2130 (see for example FIGS. 24, 27). In anembodiment, the switch mode power supply 2130 can be grounded and beseries coupled to a floating DC power source coupled in series betweenthe switch mode power supply 2130 and the electrostatic chuck 2111.

The controller 2132 can control an AC and DC output of the switch modepower supply when the switch mode power supply 2130 includes both an ACand DC power source. When the switch mode power supply 2130 is connectedin series with a DC power source, the controller 2132 may only controlthe AC output of the switch mode power supply 2130. In an alternativeembodiment, the controller 2130 can control both a DC power supplycoupled to the switch mode power supply 2130, and the switch mode powersupply 2130. One skilled in the art will recognize that while a singlecontroller 2132 is illustrated, other controllers can also beimplemented to control the AC waveform and DC offset provided to theelectrostatic chuck 2111.

The electrostatic chuck 2111 can be a dielectric (e.g., ceramic) andthus substantially block passage of DC voltages, or it can be asemiconductive material such as a doped ceramic. In either case, theelectrostatic chuck 2111 can have a second voltage V₂ on a top surface2121 of the electrostatic chuck 2111 that capacitively couples voltageto a top surface 2118 of the substrate 2106 (usually a dielectric) toform the first voltage V₁.

The plasma 2104 shape and size are not necessarily drawn to scale. Forinstance, an edge of the plasma 2104 can be defined by a certain plasmadensity in which case the illustrated plasma 2104 is not drawn with anyparticular plasma density in mind. Similarly, at least some plasmadensity fills the entire plasma processing chamber 2102 despite theillustrated plasma 2104 shape. The illustrated plasma 2104 shape isintended primarily to show the sheath 2115, which does have asubstantially smaller plasma density than the plasma 2104.

FIG. 22 illustrates another embodiment of a plasma processing system2200. In the illustrated embodiment, the switch mode power supply 2230includes a DC power source 2234 and an AC power source 2236 connected inseries. Controller 2232 is configured to control an AC waveform with aDC offset output of the switch mode power supply 2230 by controllingboth the AC power source 2236 waveform and the DC power source 2234 biasor offset. This embodiment also includes an electrostatic chuck 2211having a grid or mesh electrode 2210 embedded in the chuck 2211. Theswitch mode power supply 2230 provides both an AC and DC bias to thegrid electrode 2210. The DC bias along with the AC component, which issubstantially smaller than the DC bias and can thus be neglected,establishes a third potential V₄ on the grid electrode 2210. When thethird potential V₄ is different than a potential at a reference layeranywhere within the substrate 2206 (excluding the bottom surface 2220 ofthe substrate 2206), a chucking potential V_(chuck) and a coulombicchucking force are established which hold the substrate 2206 to theelectrostatic chuck 2211. The reference layer is an imaginary planeparallel to the grid electrode 2210. The AC waveform capacitivelycouples from the grid electrode 2210 through a portion of theelectrostatic chuck 2211, and through the substrate 2206 to control thefirst potential V₁ on a top surface 2218 of the substrate 2206. Since aplasma potential V₃ is negligible relative to a plasma sheath voltageV_(sheath), the first potential V₁ and the plasma sheath voltageV_(sheath) are approximately equal, and for practical purposes areconsidered equal. Therefore, the first potential V₁ equals the potentialused to accelerate ions through the sheath 2215.

In an embodiment, the electrostatic chuck 2211 can be doped so as to beconductive enough that any potential difference through the body of thechuck 2211 is negligible, and thus the grid or mesh electrode 2210 canbe at substantially the same voltage as the second potential V₂.

The grid electrode 2210 can be any conductive planar device embedded inthe electrostatic chuck 2211, parallel to the substrate 2206, andconfigured to be biased by the switch mode power supply 2230 and toestablish a chucking potential V_(chuck). Although the grid electrode2210 is illustrated as being embedded in a lower portion of theelectrostatic chuck 2211, the grid electrode 2210 can be located closeror further from the substrate 2206. The grid electrode 2210 also doesnot have to have a grid pattern. In an embodiment, the grid electrode2210 can be a solid electrode or have a non-solid structure with anon-grid shape (e.g., a checkerboard pattern). In an embodiment, theelectrostatic chuck 2211 is a ceramic or other dielectric and thus thethird potential V₄ on the grid electrode 2210 is not equal to the firstpotential V₁ on a top surface 2221 of the electrostatic chuck 2211. Inanother embodiment, the electrostatic chuck 2211 is a doped ceramic thatis slightly conductive and thus the third potential V₄ on the gridelectrode 2210 can be equal to the second potential V₂ on the topsurface 2221 of the electrostatic chuck 2211.

The switch mode power supply 2230 generates an AC output that can benon-sinusoidal. The switch mode power supply 2230 is able to operate theDC and AC sources 2234, 2236 in series because the DC power source 2234is AC-conductive and the AC power source 2236 is DC-conductive.Exemplary AC power sources that are not DC-conductive are certain linearamplifiers which can be damaged when provided with DC voltage orcurrent. The use of AC-conductive and DC-conductive power sourcesreduces the number of components used in the switch mode power supply2230. For instance, if the DC power source 2234 is AC-blocking, then anAC-bypass or DC-blocking component (e.g., a capacitor) may have to bearranged in parallel with the DC power source 2234. If the AC powersource 2236 is DC-blocking, then a DC-bypass or AC-blocking component(e.g., an inductor) may have to be arranged in parallel with the ACpower source 2236.

In this embodiment, the AC power source 2238 is generally configured toapply a voltage bias to the electrostatic chuck 2211 in a controllablemanner so as to effectuate a desired (or defined) ion energydistribution for the ions bombarding the top surface 2218 of thesubstrate 2206. More specifically, the AC power source 2236 isconfigured to effectuate the desired (or defined) ion energydistribution by applying one or more particular waveforms at particularpower levels to the grid electrode 2210. And more particularly, the ACpower source 2236 applies particular power levels to effectuateparticular ion energies, and applies the particular power levels usingone or more voltage waveforms defined by waveform data stored in awaveform memory (not illustrated). As a consequence, one or moreparticular ion bombardment energies may be selected to carry outcontrolled etching of the substrate 2206 (or other plasma-assistedprocesses). In one embodiment, the AC power source 2236 can make use ofa switched mode configuration (see for example FIGS. 25-27). The switchmode power supply 2230, and particularly the AC power source 2236, canproduce an AC waveform as described in various embodiments of thisdisclosure.

One skilled in the art will recognize that the grid electrode 2210 maynot be necessary and that other embodiments can be implemented withoutthe grid electrode 2210. One skilled in the art will also recognize thatthe grid electrode 2210 is just one example of numerous devices that canbe used to establish chucking potential V_(chuck).

FIG. 23 illustrates another embodiment, of a plasma processing system2300. The illustrated embodiment includes a switch mode power supply2330 for providing an AC waveform and a DC bias to an electrostaticchuck 2311. The switch mode power supply 2330 includes a DC power source2334 and an AC power source 2336, both of which can be grounded. The ACpower source 2336 generates an AC waveform that is provided to a firstgrid or mesh electrode 2310 embedded in the electrostatic chuck 2311 viaa first conductor 2324. The AC power source 2336 establishes a potentialV₄ on the first grid or mesh electrode 2310. The DC power source 2334generates a DC bias that is provided to a second grid or mesh electrode2312 embedded in the electrostatic chuck 2311 via a second conductor2325. The DC power source 2334 establishes a potential V₅ on the secondgrid or mesh electrode 2312. The potentials V₄ and V₅ can beindependently controlled via the AC and DC power sources 2336, 2334,respectively. However, the first and second grid or mesh electrodes2310, 2312 can also be capacitively coupled and/or there can be DCcoupling between the grid or mesh electrodes 2310, 2312 via a portion ofthe electrostatic chuck 2311. If either AC or DC coupling exists, thenthe potentials V₄ and V₅ may be coupled. One skilled in the art willrecognize that the first and second grid electrodes 2310, 2312 can bearranged in various locations throughout the electrostatic chuck 2311including arranging the first grid electrode 2310 closer to thesubstrate 2306 than the second grid electrode 2312.

FIG. 24 illustrates another embodiment of a plasma processing system2400. In this embodiment, a switch mode power supply 2430 provides an ACwaveform to an electrostatic chuck 2411, where the switch mode powersupply 2430 output is offset by a DC bias provided by a DC power supply2434. The AC waveform of the switch mode power supply 2430 has awaveform selected by controller 2435 to bombard a substrate 2406 withions from a plasma 2404 having a narrow ion energy distribution. The ACwaveform can be non-sinusoidal (e.g., square wave or pulsed) and can begenerated via an AC power source 2436 of the switch mode power supply2430. Chucking is controlled via the DC offset from the DC power supply2434, which is controlled by controller 2433. The DC power supply 2434can be coupled in series between ground and the switch mode power supply2430. The switch mode power supply 2430 is floating such that its DCbias can be set by the DC power supply 2434.

One skilled in the art will recognize that while the illustratedembodiment shows two independent controllers 2433, 2435, these could becombined into a single functional unit, device, or system such asoptional controller 2432. Additionally, controllers 2433 and 2435 can becoupled so as to communicate with each other and share processingresources.

FIG. 25 illustrates a further embodiment of a plasma processing system2500. The illustrated embodiment includes a switch mode power supply2530 that produces an AC waveform that can have a DC offset provided bya DC power supply (not illustrated). The switch mode power supply can becontrolled via optional controller 2535, which encompasses a voltage andcurrent controller 2537, 2539. The switch mode power supply 2530 caninclude a controllable voltage source 2538 having a voltage outputcontrolled by the voltage controller 2537, and a controllable currentsource 2540 having a current output controlled by the current controller2539. The controllable voltage and current sources 2538, 2540 can be ina parallel arrangement. The controllable current source 2540 isconfigured to compensate for an ion current between a plasma 2504 and asubstrate 2506.

The voltage and current controllers 2537, 2539 can be coupled and incommunication with each other. The voltage controller 2537 can alsocontrol a switched output 2539 of the controllable voltage source 2538.The switched output 2539 can include two switches in parallel asillustrated, or can include any circuitry that converts an output of thecontrollable voltage source 2538 into a desired AC waveform (e.g.,non-sinusoidal). Via the two switches, a controlled voltage or ACwaveform from the controllable voltage source 2538 can be combined witha controlled current output of the controllable current source 2540 togenerate an AC waveform output of the switch mode power supply 2530.

The controllable voltage source 2538 is illustrated as having a givenpolarity, but one skilled in the art will recognize that the oppositepolarity is an equivalent to that illustrated. Optionally, thecontrollable voltage and current sources 2538, 2540 along with theswitched output 2539 can be part of an AC power source 2536 and the ACpower source 2536 can be arranged in series with a DC power source (notillustrated) that is inside or outside of the switch mode power supply2530.

FIG. 26 illustrates yet another embodiment of a plasma processing system2600. In the illustrated embodiment, a switch mode power supply 2630provides an AC waveform having a DC offset to an electrostatic chuck2611. The AC component of the waveform is generated via a parallelcombination of a controllable voltage source 2638 and a controllablecurrent source 2640 connected to each other through a switched output2639. The DC offset is generated by a DC power source 2634 coupled inseries between ground and the controllable voltage source 2638. In anembodiment, the DC power source 2634 can be floating rather thangrounded. Similarly, the switch mode power supply 2630 can be floatingor grounded.

The system 2600 can include one or more controllers for controlling anoutput of the switch mode power supply 2630. A first controller 2632 cancontrol the output of the switch mode power supply 2630, for instancevia a second controller 2633 and a third controller 2635. The secondcontroller 2633 can control a DC offset of the switch mode power supply2630 as generated by the DC power source 2634. The third controller 2635can control the AC waveform of the switch mode power supply 2630 bycontrolling the controllable voltage source 2638 and the controllablecurrent source 2640. In an embodiment, a voltage controller 2637controls the voltage output of the controllable voltage source 2638 anda current controller 2639 controls a current of the controllable currentsource 2640. The voltage and current controllers 2637, 2639 can be incommunication with each other and can be a part of the third controller2635.

One skilled in the art will recognize that the embodiments above,describing various configurations of controllers relative to the powersources 2634, 2638, 2640, are not limiting, and that various otherconfigurations can also be implemented without departing from thisdisclosure. For instance, the third controller 2635 or the voltagecontroller 2637 can control a switched output 2639 between thecontrollable voltage source 2638 and the controllable current source2640. As another example, the second and third controllers 2633, 2635can be in communication with each other (even though not illustrated assuch). It should also be understood that the polarities of thecontrollable voltage and current sources 2638, 2640 are illustrativeonly and not meant to be limiting.

The switched output 2639 can operate by alternately switching twoparallel switches in order to shape an AC waveform. The switched output2639 can include any variety of switches including, but not limited to,MOSFET and BJT. In one variation, the DC power source 2634 can bearranged between the controllable current source 2640 and theelectrostatic chuck 2611 (in other words, the DC power source 2634 canfloat), and the switch mode power supply 2630 can be grounded.

FIG. 27 illustrates another embodiment of a plasma processing system2700. In this variation, the switch mode power supply 2734 again isgrounded, but instead of being incorporated into the switch mode powersupply 2730, here the DC power source 2734 is a separate component andprovides a DC offset to the entire switch mode power supply 2730 ratherthan just components within the switch mode power supply 2730.

FIG. 28 illustrates a method 2800 according to an embodiment of thisdisclosure. The method 2800 includes a place a substrate in a plasmachamber operation 2802. The method 2800 further includes a form a plasmain the plasma chamber operation 2804. Such a plasma can be formed insitu or via a remote projected source. The method 2800 also includes aswitch power operation 2806. The switch power operation 2806 involvescontrollably switching power to the substrate so as to apply a periodvoltage function to the substrate. The periodic voltage function can beconsidered a pulsed waveform (e.g., square wave) or an AC waveform andincludes a DC offset generated by a DC power source in series with aswitch mode power supply. In an embodiment, the DC power source can beincorporated into the switch mode power supply and thus be in serieswith an AC power source of the switch mode power supply. The DC offsetgenerates a potential difference between a top surface of anelectrostatic chuck and a reference layer within the substrate and thispotential difference is referred to as the chucking potential. Thechucking potential between the electrostatic chuck and the substrateholds the substrate to the electrostatic chuck thus preventing thesubstrate from moving during processing. The method 2800 furtherincludes a modulate operation 2808 in which the periodic voltagefunction is modulated over multiple cycles. The modulation is responsiveto a desired (or defined) ion energy distribution at the surface of thesubstrate so as to effectuate the desired (or defined) ion energydistribution on a time-averaged basis.

FIG. 29 illustrates another method 2900 according to an embodiment ofthis disclosure. The method 2900 includes a place a substrate in aplasma chamber operation 2902. The method 2900 further includes a form aplasma in the plasma chamber operation 2904. Such a plasma can be formedin situ or via a remote projected source. The method 2900 also includesa receive at least one ion-energy distribution setting operation 2906.The setting received in the receive operation 2906 can be indicative ofone or more ion energies at a surface of the substrate. The method 2900further includes a switch power operation 2908 in which power to thesubstrate is controllably switched so as to effectuate the following:(1) a desired (or defined) distribution of ion energies on atime-averaged basis; and (2) a desired chucking potential on atime-averaged basis. The power can have an AC waveform and a DC offset.

Calibration

There may be instances where it is desirable to test an accuracy of setpoints such as bias compensation current and the periodic voltagefunction. FIG. 51 illustrates a schematic diagram depicting an exemplaryembodiment of an apparatus for calibrating a bias supply 5100 (alsoreferred to herein as an eV source). The bias supply 5100 can include apower supply 5102 (e.g., a switch-mode power supply), an ion currentcompensation component 5104 (e.g., a current supply), and a controller5106 for controlling the power supply 5102 and the ion currentcompensation component 5104. The bias supply 5100 can be coupled to acalibration component 5150 via a power path 5130 (e.g., a power cable),where the calibration component 5150 includes components for emulating aload such as a plasma load. In particular the calibration component 5150can include a load emulator 5152 able to emulate such electricalcharacteristics as ion energy (or sheath voltage), ion current, sheathcapacitance (C_(sheath)), and effective capacitance, to name a fewnon-limiting examples. For instance, ion current can represent theelectrical characteristics of plasma density. The calibration component5150 can also include a measurement component 5154 and an analysiscomponent 5156.

The bias supply 5100 can generate a modified periodic voltage functionthat if provided to a plasma load is expected to achieve an expected ionenergy and an expected ion current. For calibration this modifiedperiodic voltage function can be provided to the calibration component5150, and in particular to the load emulator 5152, where measurementscan be made to determine what ion energy and ion current would actuallybe achieved if the modified periodic voltage function were provided to aplasma load. These measured values are compared to the expected valuesand differences (error values) can be reported back to the user.Alternatively, the error values can be returned to the bias supply 5100in order to enable automated calibration of the bias supply 5100.

Expected values can be derived as discussed in previous sections of thisdisclosure from the modified periodic voltage function. This can includemeasuring a modified periodic voltage function at a node 5112, anddetermining expected values including at least one of the following: anexpected ion current, an expected ion energy, an expected sheathcapacitance. The expected values can also correspond to control inputsto the controller 5106, such as a defined ion current or a defined ionenergy as provided via user selection. In one embodiment, the controller5106 can measure the modified periodic voltage function at node 5112.

For purposes of this disclosure, a user selection can includemanually-entered values or values provided by a program or software. Forinstance, a program may be written that includes a table of combinationsof ion energy and ion current. When the controller 5106 runs theprogram, it can control the power supply 5102 and the ion currentcompensation component 5104 so as to try to achieve each combination inthe table (or a subset thereof). In this way, the program can be used tocalibrate the bias supply 5100 for a variety of different set pointsthat a user may select during actual processing.

The expected values can be sent from the controller 5106 to thecalibration component 5150, and in particular the analysis module 5156,via a first data path 5132. Alternatively the power supply 5102 and/orthe ion current compensation 5104 can provide set point values to theanalysis component 5156. For instance the power supply 5102 can providea voltage set point for the periodic voltage function. As anotherexample the ion current compensation component 5104 can provide an ioncompensation current value. While the expected values are illustrated aspassing along the first data path 5132, in other embodiments other datapaths may be used, such as modulating data along the power path 5130.

The modified periodic voltage function is provided to the calibrationcomponent 5150, which passes it into the load emulator 5152. The loademulator 5152 can emulate current and capacitive characteristics of aplasma load. In some cases, impedance and rectifying characteristics ofa plasma load can also be emulated. The current characteristics caninclude the ion current. The capacitive characteristics can include asheath capacitance and an effective capacitance where the effectivecapacitance is that of the substrate support (or e-chuck in some cases)along with the substrate and optionally stray capacitances. Therectifying characteristics can represent the rectifying nature of thesheath.

The measurement component 5154 measures current and one or more voltagesof the load emulator 5152 in order to determine measured values of ioncurrent, ion energy, and optionally sheath capacitance and effectivecapacitance. Other voltage and current waveforms in the load emulator5152 can also be measured. For instance, the measurement component 5154can measure the modified periodic voltage function provided to the loademulator 5152 from the bias supply 5100. Details of the load emulatorand these measurements will be discussed with reference to FIG. 52.

The analysis module 5156 compares these measured values to correspondingexpected values. In some embodiments, an expected sheath capacitance andan expected effective capacitance can be compared to measured values ofthe same. In an embodiment, the analysis module 5156 can perform thesecomparisons via one or more comparators. The comparisons can generateerror values or the difference between an expected and a measured value.

The error values can be reported, stored in a memory of the calibrationcomponent 5150, or provided to the bias supply 5100 via a second datapath 5134. The error values can be converted to calibration data in thecontroller 5106 and used by the controller 5106 to adjust instructionsto the power supply 5102 and the ion current compensation component5104. In particular, the calibration data indicates by how much thecontroller 5106 is to adjust its instructions in order to achieve theexpected values. Alternatively, the error values can be converted tocalibration data in the analysis module 5156 and then passed to the biassupply 5100 via the second data path 5134. The error values or thecalibration data can also be stored in a calibration data store 5108.

Reporting can involve rendering the error values to a display forinspection by a user or printing the results to paper, to name twonon-limiting examples. If error values are reported to the user, thenthe user can check to ensure that all aspects of the bias supply 5100are operating within acceptable limits. For instance if the sheathcapacitance measured in the load emulator 5152 is lower than theexpected sheath capacitance, then the power supply 5102 can be checkedto ensure that the proper output voltage is being generated.Alternatively, the user can take the error values into account whenselecting ion energy and ion current during actual processing.

If the error values are passed back to the bias supply 5100, then theycan be used in an automated calibration of the bias supply 5100. As anexample, if the ion energy measured in the load emulator 5152 is lowerthan the expected ion energy, then the controller 5106 can use thecalibration data to adjust its instructions to the power supply 5102 inorder to realize the expected ion energy. In some embodiments the biassupply 5100 and the calibration component 5150 can be synced such thecurrent and voltage can be compared on a pulse by pulse basis.

FIG. 52 illustrates a load emulator 5252 of the calibration component5150 illustrated in FIG. 51. The load emulator 5252 emulates electricalcharacteristics of the plasma sheath as well as the substrate support.This is performed by the components surrounded by dotted line 5256, andcan emulate impedance, capacitance, and rectification characteristics ofthe plasma sheath. The load emulator 5252 can also include one or moreoptional components outside the dotted line 5256 that are configured toemulate other electrical characteristics of the system such as abias-to-load cable connection and effects of a source supply, to nametwo. The load emulator 5252 is part of the calibration component 5150,and a measurement component (e.g., measurement component 5154) (notillustrated) can measure current, voltage, and capacitance within theload emulator 5252 in order to compare these measured values withexpected values provided by a bias supply (not illustrated). Forinstance, measurements of ion current, ion energy (or sheath voltage),and sheath capacitance can be made.

The load emulator 5252 can include a current source 5264 emulating theion current in the sheath. A sheath capacitance component 5262 canemulate the sheath capacitance, where the sheath is a region of theplasma with a much greater density of positive ions than electrons andis also the accelerating portion of the plasma. A rectifying component5260 can emulate the rectifying effects of the sheath.

The ion current can be measured as a current from the current source5264, or the ion current can be accessed as the current source 5264 setpoint. Measuring the sheath voltage across the sheath capacitor 5262, orthe voltage between the node 5266 and ground, gives a voltage emulatingthe sheath voltage. The sheath voltage is also the voltage that inpractice would be seen on the substrate surface, and therefore has anexpected waveform shape. The sheath voltage measurement can be comparedto the expected shape of the sheath voltage to provide indications offaults or abnormalities in the bias supply or the source. Also, theamount of time that the system takes to identify a fault or anomaly canindicate a problem. The measurement component can perform thesemeasurements and/or access set points of the current source 5264, thesheath capacitance component 5262, or the effective capacitancecomponent 5258.

The current source 5264 can be a variable current source and can beswept across a range of currents for a given sheath capacitance asestablished by the sheath capacitance component 5262. The sheathcapacitance component 5262 can also be adjusted for different sheathcapacitances. For instance, given an expected sheath capacitance, thesheath capacitance component 5262 can be set to the value of theexpected sheath capacitance. The sheath voltage can be measured at node5266, and compared to the expected sheath voltage to determine whetherthe bias supply is accurately calibrated or not.

The sheath capacitance component 5262 can be embodied by a variablecapacitance circuit such as a bank of switched, discrete, capacitors. Insome embodiments, the bank of capacitors can include individuallycalibrated capacitors. In an embodiment, the capacitors are ultra lowloss vacuum capacitors and ultra pure ceramic capacitors.

The rectifying component 5260 can be implemented as a diode, and in theillustrated embodiment it is arranged in parallel with the sheathcapacitance component 5262. The rectifying component 5260 can be forwardbiased from the node 5266 to ground, and reverse biased from the groundto the node 5266. When the load emulator 5252 is operating as if aplasma were ignited, the rectifying component 5260 will be reversebiased and the voltage at node 5266 will be negative relative to ground(except for a small portion of each cycle which is positive).

An optional cable 5230 can be designed to mimic (or be identical to) acable that would typically connect the bias supply to the substratesupport. In other embodiments, circuitry inside the load emulator 5252can emulate the cable. For instance, a cable emulating component 5252can be implemented, or the combination of the cable emulating component5252 and a cathode connection emulating component 5254. The cathodeconnection can also be thought of as the connection between the cableand the substrate support, or the connection between the cable and thegrid electrode. The cable emulating component 5252 can includeresistive, capacitive, and inductive components designed to emulate theelectrical characteristics of the cable. The cathode connectionemulating component 5254 can also include impedance, capacitance, andinductance components designed to emulate electrical characteristics ofthe cathode connection of the cable. The power path 5130 in FIG. 51 canbe implemented as either the cable 5230, the cable emulating component5252, or the combination of the cable emulating component 5252 and thecathode connection emulating component 5254.

The load emulator 5252 is also configured to emulate aspects of thesource as represented by a parallel capacitance component 5268, a sourcechuck component 5270, and a source component 5272. The parallel reactivecomponent 5268 can emulate an e-chuck or other capacitive, inductive, orcapacitive and inductive component. The source chuck component 5270emulates electrical characteristics of a chuck that couples power fromthe source to the plasma load. The source component 5272 emulateselectrical characteristics of the power supplied to the plasma load inorder to ignite and sustain the plasma. In some embodiments the sourcecomponent 5272 can further emulate a filter

The effective capacitance component 5258 can be designed to emulateelectrical characteristics of the e-chuck. For instance a variablecapacitance circuit can be used, and in particular in parallelarrangement of switchable capacitors. One might vary the capacitance ofthe effective capacitance component 5258 in order to emulate differenttypes of substrate supports (e.g., dielectric or conductive). Thecapacitance of the effective capacitance component 5258 can comprise abank of switchable discrete capacitors such as ultra low loss vacuumcapacitors or ultra pure ceramic capacitors. In some embodiments, theeffective capacitance component 5258 can emulate at least a seriescapacitance between a termination of the cable (between the bias supplyand the substrate support) and the substrate (and in particular, the topsurface of the substrate). In some embodiments, the termination of thecable is a grid electrode (recall grid electrode 2210 in FIG. 22). Ininstances where a substrate is heavily doped and thus has a highcapacitance from a bottom to top surface, the series capacitance may bedominated by the capacitance between a termination of the cable and abottom surface of the substrate.

Although the illustrated bias supply 5100 includes a power supply 5102and an ion current compensation component 5104, the calibrationcomponent 5150 can also be used in conjunction with other bias supplies5100 such as a linear amplifier. This is because the calibrationcomponent 5150, and in particular the load emulator 5152 is agnosticwith regard to the type of the bias supply or the source. In the case ofa linear amplifier being used for the bias supply 5100 there may be noaccounting for an ion compensation current or a sheath capacitance.

The following discusses methods for calibrating the bias supply 5100while referencing method blocks illustrated in FIG. 53. The bias supply5100 can receive a user selection or automated selection of a definedion energy and a defined ion current (Block 5302). The controller 5106can then instruct the power supply 5102 to produce a periodic voltagefunction and to instruct the ion current compensation component 5104 tomodify the periodic voltage function with an ion compensation current soas to generate a modified periodic voltage function based on theselected defined ion energy and ion current at the node 5112 (Block5304). The power path connecting the bias supply 5100 to the calibrationcomponent 5150 can deliver the modified periodic voltage function to thecalibration component 5150 (Block 5306). The bias supply 5100 canfurther deliver the selected defined ion energy and ion current to thecalibration component 5150 via a data path 5132 (Block 5308). Thecalibration component can then generate calibration data and return thecalibration data to the bias supply 5100 via a second data path 5134.The bias supply 5100 can receive the calibration data (Block 5310), andoptionally store the calibration data at a calibration data store 5108(Block 5312).

The controller 5106 can then use the calibration data to adjust itsinstructions to the power supply 5102 and its instructions the ioncurrent compensation component 5104 for a given selection of a definedion energy and defined ion current in order to more accurately generatethe selected defined ion current and selected defined ion energy in aplasma during processing.

The following discusses methods for calibrating the bias supply 5100while referencing method blocks illustrated in FIG. 54. The bias supply5100 can generate a modified periodic voltage function based on anautomated selection of, or user selection of, a defined ion energy and adefined ion current. These selections generate an expected ion energyand an expected ion current. The calibration component 5150 can receivethe modified periodic voltage function, the expected ion energy, and theexpected ion energy. In particular the modified periodic voltagefunction can be received at the load emulator 5152 (Block 5402). Theexpected ion energy and expected ion current can be received at theanalysis module 5156 (Block 5404). The measurement component 5154 canthen make measurements within the load emulator 5152 and can providethese measured values to the analysis module 5156. In particular, themeasurement module 5154 can access the current generated by the currentsource 5264 of the load emulator 5152 (Block 5406). Also the measurementmodule 5154 can measure a voltage across a sheath capacitance component5262 of the load emulator 5152 (Block 5408). These measured values canbe passed to the analysis module 5156 where they are compared to theexpected values provided by the bias supply 5100 (Block 5410). If thereis no difference between the measured and expected values, then theanalysis module 5156 may not generate any calibration data nor reportany error values (Block 5412). On the other hand if there is adifference between the measured and expected values, then the analysismodule 5156 can report the error values (Block 5416) and optionallygenerate calibration data (Block 5416) to be passed back to the biassupply 5100.

In the bias supply 5100 the calibration data can be stored in theoptional calibration data store 5108. The controller 5106 can thenselect a new defined ion energy and ion current (Block 5302) and theprocess can repeat. In other embodiments the above described method maybe performed for one or more of the following values and can sweep anyone or more of the following: periodic voltage function, ioncompensation current, ion energy, ion current, sheath voltage, andeffective capacitance. For instance the controller 5106 can instruct thepower supply 5102 to produce a periodic voltage function and to instructthe ion current compensation component 5104 to modify the periodicvoltage function with an ion compensation current. At the same time theload emulator 5152 can set the sheath capacitances to a plurality ofvalues in order to emulate a variety of electrical conditions within aplasma that may be seen during actual processing. As a further example,the method block 5310 in FIG. 53 could involve the receiving ofcalibration data relative to a plurality of ion current values at theload emulator 5152 used for a given set point of the power supply 5102and a given set point of the ion current compensation component 5104.

Chamber Calibration

Once the bias supply has been calibrated, it may be desirable tocalibrate the chamber. In one embodiment, a calibrated bias supply canbe coupled to a non-calibrated plasma processing chamber, and inparticular to a substrate support 5512 as illustrated in FIG. 55. Thesystem of FIG. 55 will be discussed in combination with method blocksillustrated in FIG. 56. A calibrated bias supply 5100 can provide aconstant voltage and current, or a modified periodic voltage function,to a substrate support 5512, which supports a substrate 5514. In someembodiments, the calibrated bias supply 5100 can couple to the substratesupport 5512 at a node 5520, which can also be accessed for makingcapacitance measurements.

The illustrated series capacitance 5516, C_(series), representscapacitance between a point in the substrate support 5512, such as thegrid electrode 2210 in FIG. 22, and a bottom surface of the substrate5514. Alternatively, the series capacitance 5516 can represent acapacitance between the node 5520 and a bottom surface of the substrate5514. Optionally, the series capacitance 5516 can represent thecapacitance between a point in the substrate support 5512 (or the node5520), and a top surface of the substrate 5514, where the substrate haslow conductivity (e.g., when lightly doped). The illustrated parallelcapacitance 5518 can represent a capacitance between the point in thesubstrate support 5512 (or the node 5520) and ground.

Calibration of the plasma processing chamber 5510 involves determinationof an effective capacitance, C_(effective). As discussed earlier, theeffective capacitance, can be used to control ion energy, IEDF width,and IEDF shape during processing (as discussed earlier). The effectivecapacitance, C_(effective), is a sum of series capacitance, parallelcapacitance, and stray capacitance as show in Equation 9 as follows:C _(effective) =C _(series) +C _(parallel) +C _(stray)  (Equation 9)

Where C_(stray) is stray capacitance inside the bias supply 5500 andC_(series) 5516 and C_(parallel) 5518 are representative capacitancessymbolized in FIG. 55. In some embodiments, C_(parallel) 5518 caninclude stray capacitances of the plasma processing chamber 5510.C_(stray) can be determined from knowledge of the circuit design of thebias supply 5500. C_(stray) can also be measured. Alternatively,C_(stray) can be determined from knowledge of the circuit design of thebias supply 5500 and then checked via measurement. One of skill in theart will recognize that C_(series) and C_(parallel) are illustrated formodeling purposes only and do not represent actual capacitors or theexact locations of the capacitive effects that they represent. Theeffective capacitance, C_(effective), is the capacitance seen by thebias supply 5500. The series capacitance, C_(series), 5516 and theparallel capacitance, C_(parallel), 5518 can be measured as follows.

The bias supply 5500, in some embodiments, can first be calibrated(Block 5602) as described relative to FIGS. 51-54. In one embodiment,the substrate 5514 can be grounded (Block 5604), for instance by makinga conductive connection 5515 between the substrate 5514 and an innerwall of the plasma processing chamber 5510, which is grounded. Theconductive connection 5515 can take a variety of forms. For instance,the conductive connection 5515 can be an axially or radially-arrangedconductive component that touches an inner wall of the plasma processingchamber 5510. This is done to avoid inductive parasitics in thegrounding component. In another example, an optional plasma 5522 can beignited in order to short the substrate 5514 to ground. If the optionalplasma 5522 is used for the conductive connection 5515, then in oneinstance, a conductive gas, such as an Argon-dominated gas, can bereleased into the plasma processing chamber 5510. In anotherplasma-based embodiment, the source supply 5550 power can be increasedsuch that a dense plasma 5522 is formed thus enhancing conductivity ofthe conductive connection 5515. Furthermore, the conductivity of theoptional plasma 5522 can be increased by creating a low pressureatmosphere in the plasma processing chamber 5510. These are just a fewof the many embodiments that the conductive connection 5515 can take.

When the substrate 5514 is grounded via some embodiment of theconductive connection 5515, the bias supply 5500 can provide a constantvoltage and current, or a modified periodic voltage function, to thesubstrate support 5512 while there is no process running (although thesource supply 5550 can be on or off depending on whether the optionalplasma 5522 is being used for the conductive connection 5515). With thesubstrate 5514 grounded, current from the bias supply 5500 primarilypasses through the series capacitance 5516, such that measurements ofcapacitance taken at node 5520, or remotely via the bias supply 5500 asdiscussed previously, provide the series capacitance 5516 (Block 5606).

To measure the parallel capacitance 5518, the conductive connection 5515can be removed (Block 5608). For instance, the optional plasma 5522 canbe turned off, or a solid conductive connection can be removed. With theconductive connection 5515 removed, current from the bias supply 5500primarily passes through the parallel capacitance 5518. Measurementstaken at node 5520 (Block 5610), or remotely via the bias supply 5500,can provide the parallel capacitance 5518.

Having measured the series and parallel capacitances 5516, 5518, andsince C_(stray) is known, and/or can be measured, the effectivecapacitance, C_(effective), can be calculated (Block 5612) according toEquation 9, and then used to control the ion energy, IEDF width, andother aspects of a plasma during processing.

As noted, C_(series) 5516 and C_(parallel) 5518 can be measured, onefrequency at a time, via an impedance or capacitance sensor at node5520, or remotely, via the bias supply 5500. In each of the embodimentsto be discussed in this paragraph C_(series) 5516 is measured with theconductive connection 5515 grounding the substrate 5514, andC_(parallel) 5518 measured without the conductive connection 5515. Fordirect measurements at node 5520, impedance or capacitance sensors caninclude an impedance analyzer or a network analyzer. An impedanceanalyzer may only be able to make one frequency measurement at a time,while the network analyzer may be able to make multiple frequencymeasurements at a time. In another embodiment, remote measurements ofC_(series) 5516 and C_(parallel) 5518 can be made by providing avoltage, such as the modified periodic voltage function, from the biassupply 5500 to the node 5520 and analyzing the voltage to determineC_(series) 5516 and C_(parallel) 5518. This third and remote methodenables multiple voltages and multiple frequencies to be studied.

So far, embodiments have been described for chamber calibration when aprocess is not running. Yet, sometimes it is preferable to calibrate theplasma processing chamber 5510 during a process run. In the followingembodiments, calibration is performed during a test recipe or actualprocessing. The system of FIG. 55 will now be described in combinationwith parenthetical references to operations in FIG. 57.

Again, the bias supply 5500 can be calibrated (Block 5702), and thesubstrate 5514 can be grounded (Block 5704) via the conductiveconnection 5515. The process recipe can begin (Block 5705), forinstance, by releasing a gas (e.g., argon) into the plasma processingchamber 5510 and/or igniting the optional plasma 5520. Measurements ofC_(series) 5516 (Block 5706) can be made, the conductive connection 5515can be removed (Block 5708), and then C_(parallel) 5618 can be measured(Block 5710). Equation 9 can then be used to calculate the effectivecapacitance, C_(effective) in terms of C_(series) 5516 and C_(parallel)5518 (Block 5712).

The above-described calibrations can be performed periodically over timeto ensure consistency during the lifetime of a process. Suchcalibrations can also be performed to ensure that processes aresimilarly performed in different chambers. In some embodiments,parameters may be known for a properly working process and/or chamber,and measured values during a calibration can be compared to these known(or reference) values in order to identify problems with the chamber orthe process. The parameters can include any portion of the modifiedperiodic voltage function. For instance, the slope between the pulsescan be compared between a reference waveform and an actual waveform. Theactual waveform can be taken from a test run or from an actualprocessing run. In other words, real-time observation of processconsistency is possible during test runs and even during productionprocessing.

In conclusion, the present invention provides, among other things, amethod and apparatus for selectively generating desired (or defined) ionenergies using a switch-mode power supply. Those skilled in the art canreadily recognize that numerous variations and substitutions may be madein the invention, its use, and its configuration to achievesubstantially the same results as achieved by the embodiments describedherein. Accordingly, there is no intention to limit the invention to thedisclosed exemplary forms. Many variations, modifications, andalternative constructions fall within the scope and spirit of thedisclosed invention.

What is claimed is:
 1. A method of calibrating a bias supply configuredto generate a potential on a top surface of a substrate during plasmaprocessing of the substrate, the method comprising: emulating a plasmasheath capacitance with a variable capacitance circuit of a plasma loademulator without generating any plasma; emulating plasma ion currentwith a variable current source without generating any plasma; receivinga modified periodic voltage function from the bias supply comprisingpulses and a portion between the pulses; receiving an expected ionenergy; receiving an expected ion current; delivering the modifiedperiodic voltage function to a plasma load emulator; measuring a voltageacross the variable capacitance circuit of the plasma load emulator;applying a known current from the variable current source of the plasmaload emulator to the variable capacitance circuit to emulate the ioncurrent; comparing the voltage across the variable capacitance circuitof the plasma load emulator to the expected ion energy and determiningan ion energy error from this comparing; comparing the known currentfrom the variable current source of the plasma load emulator to theexpected ion current and determining an ion current error from thiscomparing; generating calibration data with the ion energy error and theion current error; and storing the calibration data in a calibrationdata store in the bias supply, wherein the calibration data issubsequently utilized to more accurately effectuate ion energy in anactual plasma during the plasma processing of the substrate.
 2. Themethod of claim 1, further comprising receiving an expected sheathcapacitance, accessing a sheath capacitance of the variable capacitancecircuit of the plasma load emulator, comparing the sheath capacitance tothe expected sheath capacitance of the plasma load emulator, determininga sheath capacitance error from the third comparing, and reporting thesheath capacitance error.
 3. The method of claim 1, wherein the ioncurrent error and the ion energy error are used to calibrate a biassupply that generates the modified periodic voltage function.
 4. Themethod of claim 1, wherein the ion energy error and the ion currenterror are calculated values.
 5. The method of claim 1, wherein the ionenergy error and the ion current error are measured values.
 6. A systemcomprising: a bias supply providing a modified periodic voltage, thebias supply comprising: a power supply configured to provide a periodicvoltage function to an output; an ion current compensation componentcoupled to the output and configured to modify the periodic voltagefunction with an ion compensation current so that the bias supplyprovides the modified periodic voltage function; and a controllerconfigured to provide instructions to the power supply to adjust theperiodic voltage function and to provide instructions to the ion currentcompensation component to adjust the ion compensation current; acalibration component, separate from the bias supply and coupled to theoutput to receive the modified periodic voltage function, thecalibration component comprising: a load emulator having: circuitryconfigured to emulate impedance, rectifying effects, ion current andcapacitive characteristics of a plasma load without generating anyplasma, the load emulator further configured to receive the modifiedperiodic voltage function, and wherein; the capacitive characteristicscomprise a sheath capacitance and an effective capacitance, and thecircuity configured to emulate rectifying effects comprises reversebiased components when the load emulator emulates a plasma load withoutgenerating any plasma; a measurement component configured to make one ormore measurements of the modified periodic voltage function as itinteracts with the circuitry of the load emulator; and an analysiscomponent configured to generate and store calibration data by comparingat least one measured value from the measurement component and at leastone expected value from the bias supply wherein the calibration data issubsequently utilized to more accurately effectuate ion energy in anactual plasma during plasma processing.
 7. The system of claim 6,wherein the ion current error is calculated as a difference between anexpected ion current provided by the bias supply and a measured currentprovided by the measurement component, where the measured current isequivalent to an ion current.
 8. The system of claim 7, wherein the loademulator includes a current source configured to emulate an ion currentin a plasma load.
 9. The system of claim 7, wherein the measured valueequivalent to an ion current is an output current of the current source.10. The system of claim 9, wherein the output current of the currentsource emulates an electrical characteristic of plasma density.
 11. Thesystem of claim 7, wherein the analysis component is further configuredto determine an ion energy error by comparing at least one measuredvalue from the measurement component and at least one expected valuefrom the bias supply.
 12. The system of claim 11, wherein the ion energyerror is calculated as a difference between an expected ion energyprovided by the bias supply and a measured value equivalent to an ionenergy provided by the measurement component.
 13. The system of claim12, wherein the load emulator includes a sheath capacitance componentconfigured to emulate the sheath capacitance in the plasma load.
 14. Thesystem of claim 13, wherein the measured value equivalent to the ionenergy is the voltage across the sheath capacitance component.
 15. Thesystem of claim 7, wherein the load emulator further comprises aneffective capacitance component configured to emulate the effectivecapacitance of the plasma load.
 16. The system of claim 15, wherein theeffective capacitance component is configured to emulate a capacitanceof a substrate support and one or more stray capacitances.
 17. Thesystem of claim 6, wherein the load emulator further comprises arectifying component configured to emulate the rectifying effects of aplasma sheath.
 18. The system of claim 17, wherein the rectifyingcomponent is arranged in parallel to the sheath capacitance component,and wherein the voltage across the sheath capacitance is also thevoltage across the rectifying component.
 19. The system of claim 6,further comprising a cable emulation component configured to emulateelectrical characteristics of a power path that would be used to couplethe modified periodic voltage function to a substrate support of aplasma load.
 20. The system of claim 6, wherein the controller providesinstructions to the power supply and the ion current compensationcomponent based on the ion current error calculated by the analysiscomponent.
 21. A system comprising: a bias supply that generates amodified periodic voltage function, wherein the modified periodicvoltage function comprises periodic pulses with a sloped portion betweenthe pulses, wherein the slope of the sloped portion between the pulsesis controlled via an ion compensation current; and a calibrationcomponent, separate from the bias supply, the calibration component isdisposed to receive the modified periodic voltage function and includesvoltage and current sensors to measure a voltage and a current,respectively, of the modified periodic voltage function in a loademulator, the voltage emulating a substrate voltage associated with aplasma load without generating any plasma, the current emulating an ioncurrent in the plasma load without generating any plasma, and furtheremulating rectifying effects, wherein the rectifying effects areemulated through reverse biased rectifying components when the loademulator emulates a plasma load without generating any plasma.
 22. Thesystem of claim 21, wherein the calibration component reports a measuredion current based on the measured current.
 23. The system of claim 21,wherein the calibration component reports a measured ion energy based onthe measured voltage.
 24. The system of claim 21, wherein thecalibration component measures a first capacitance across an effectivecapacitance component of the load emulator.
 25. The system of claim 24,wherein the calibration component reports a measured effectivecapacitance based on the measured first capacitance.
 26. The system ofclaim 21, wherein the calibration component measures a secondcapacitance across a sheath capacitance component of the load emulator.27. The system of claim 26, wherein the calibration component reports ameasured sheath capacitance based on the measured second capacitance.28. A calibration component to calibrate a bias supply comprising: aload emulator configured to receive a modified periodic voltagefunction, the load emulator including: a variable capacitance circuit toemulate a plasma sheath capacitance without generating any plasma; avariable current source to emulate plasma ion current without generatingany plasma; and circuity configured to emulate plasma rectifying effectscomprising components that are reverse-biased when the load emulatoremulates a plasma load without generating any plasma a measurementcomponent configured to measure at least a current from the variablecurrent source and a voltage within the load emulator as the modifiedperiodic voltage function interacts with circuitry within the loademulator; and an analysis component configured to compare the measuredcurrent and the measured voltage to an expected current and an expectedvoltage to generate calibration data, wherein the calibration data issubsequently utilized by the bias supply to more accurately effectuateion energy in an actual plasma during plasma processing.